Long-Term Efficacy and Safety of Insulin and Glucokinase Gene Therapy for Diabetes: 8-Year Follow-Up in Dogs

Advances and challenges of the cell-based therapies among diabetic patients

Diabetes mellitus is a significant global public health challenge, with a rising prevalence and associated morbidity and mortality. Cell therapy has evolved over time and holds great potential in diabetes treatment. In the present review, we discussed the recent progresses in cell-based therapies for diabetes that provides an overview of islet and stem cell transplantation technologies used in clinical settings, highlighting their strengths and limitations. We also discussed immunomodulatory strategies employed in cell therapies. Therefore, this review highlights key progresses that pave the way to design transformative treatments to improve the life quality among diabetic patients.

The underlying causes, treatment options of gut microbiota and food habits in type 2 diabetes mellitus: a narrative review

Type 2 diabetes mellitus is a long-lasting endocrine disorder characterized by persistent hyperglycaemia, which is often triggered by an entire or relative inadequacy of insulin production or insulin resistance. As a result of resistance to insulin (IR) and an overall lack of insulin in the body, type 2 diabetes mellitus (T2DM) is a metabolic illness that is characterized by hyperglycaemia. Notably, the occurrence of vascular complications of diabetes and the advancement of IR in T2DM are accompanied by dysbiosis of the gut microbiota. Due to the difficulties in managing the disease and the dangers of multiple accompanying complications, diabetes is a chronic, progressive immune-mediated condition that plays a significant clinical and health burden on patients. The frequency and incidence of diabetes among young people have been rising worldwide. The relationship between the gut microbiota composition and the physio-pathological characteristics of T2DM proposes a novel way to monitor the condition and enhance the effectiveness of therapies. Our knowledge of the microbiota of the gut and how it affects health and illness has changed over the last 20 years. Species of the genus Eubacterium, which make up a significant portion of the core animal gut microbiome, are some of the recently discovered 'generation' of possibly helpful bacteria. In this article, we have focused on pathogenesis and therapeutic approaches towards T2DM, with a special reference to gut bacteria from ancient times to the present day.

Research progress on the mechanism of TCM regulating intestinal microbiota in the treatment of DM mellitus

In recent years, with the improvement of people's living standards, the incidence of DM has increased year by year in China. DM is a common metabolic syndrome characterized by hyperglycemia caused by genetic, environmental and other factors. At the same time, long-term suffering from DM will also have an impact on the heart, blood vessels, eyes, kidneys and nerves, and associated serious diseases. The human body has a large and complex gut microbiota, which has a significant impact on the body's metabolism. Research shows that the occurrence and development of DM and its complications are closely related to intestinal microbiota. At present, western medicine generally treats DM with drugs. The hypoglycemic effect is fast and strong, but it can have a series of side effects on the human body. Compared with western medicine, Chinese medicine has its unique views and methods in treating DM. TCM can improve symptoms and treat complications by improving the imbalance of microbiota in patients with DM. Its characteristics of health, safety, and reliability are widely accepted by the general public. This article reviews the relationship between intestinal microbiota and DM, as well as the mechanism of TCM intervention in DM by regulating intestinal microbiota.

Generation of a Beta-Cell Transplant Animal Model of Diabetes Using CRISPR Technology

Since insulin deficiency results from pancreatic beta-cell destruction, all type 1 and most type 2 diabetes patients eventually require life-long insulin injections. Insulin gene synthesis could also be impaired due to insulin gene mutations as observed in diabetic patients with MODY 10. At this point, insulin gene therapy could be very effective to recompense insulin deficiency under these circumstances. For this reason, an HIV-based lentiviral vector carrying the insulin gene under the control of insulin promoter (LentiINS) was generated, and its therapeutic efficacy was tested in a beta-cell transplant model lacking insulin produced by CRISPR/Cas9-mediated genetically engineered pancreatic beta cells. To generate an insulin knockout beta-cell transplant animal model of diabetes, a dual gene knockout plasmid system involving CRISPR/Cas9 was transfected into a mouse pancreatic beta cell line (Min6). Fluorescence microscopy and antibiotic selection were utilized to select the insulin gene knockout clones. Transplantation of the genetically engineered pancreatic beta cells under the kidney capsule of STZ-induced diabetic rats revealed LentiINS- but not LentiLacZ-infected Ins2KO cells transiently reduced hyperglycemia similar to that of MIN6 in diabetic animals. These results suggest LentiINS has the potential to functionally restore insulin production in an insulin knockout beta-cell transplant animal model of diabetes.

Progress toward molecular therapy for diabetes mellitus: A focus on targeting inflammatory factors

Diabetes mellitus (DM) has been the most prevalent global metabolic disease, turning into a serious risk for human health. Several researches have recorded a role for inflammation and immunity in the pathogenesis of both in T1DM and in T2DM. Lots of chemical agents are available to control and to cure diabetic patients, which are not always sufficient for euglycemia maintenance and late stage diabetic complications avoidance. Therefore, newborn therapeutic methods to refine clinical outcomes in DM are required. Nucleic-acid-based therapy also known as gene expression level regulator within the target cells has been calculated to be promising in various diseases. Thus, pronounced attempts have been dedicated to develop new targeted molecular therapy aimed at improving insulin resistance in DM. This review mainly focuses on recent progress in DM molecular therapy and whether, has potential efficacy against inflammatory mediators involved in DM.

Evaluation of hypoglycemic therapeutics and nutritional supplementation for type 2 diabetes mellitus management: An insight on molecular approaches

OBJECTIVE

This review aims to summarize the current management of type 2 diabetes principles, including oral hypoglycemic agents, types of insulin administration, diet maintenance, and various molecular approaches.

METHODS

A literature search was conducted in different databases such as Scopus, ScienceDirect, Google Scholar, and Web of Science by using the following keywords: type-2 diabetes mellitus (T2DM), first-line and second-line treatment, oral hypoglycemic agents, insulin administration, diet/nutritional therapy, gene and stem cell therapy, and diabetic complications.

RESULTS

The first-line treatment of T2DM includes administering oral hypoglycemic agents (OHAs) and second-line treatment by insulin therapy and some OHAs like Sulfonylurea's (SU). The oral hypoglycemic or oral antidiabetic drugs have the function of lowering glucose in the blood. Insulin therapy is recommended for people with A1C levels > 7.0, and insulin administration is evolved drastically from the syringe, pump, pen, inhalation, insulin jet, and patch. The use of OHAs and insulin therapy during glycemic control has a severe effect on weight gain and other side effects. Hence, diet maintenance (macro and micronutrients) and nutritional therapy guidelines were also reviewed/recommended for safe T2DM management. Besides, the recent progress in molecular approaches that focuses on identifying new targets for T2DM (i.e.) consisting of gene therapy, stem cell therapy, and the modulation of insulin signaling pathways for the regulation of glucose storage and uptake also discussed.

CONCLUSION

The analysis of all these key factors is necessary to develop a potential agent to cure T2DM and suggest that a combination of therapies will pave the way for advanced management of T2DM.

Future directions in insulin therapy

Insulin therapy has a long history at the cutting edge of technological development through purification, extended-action, molecular chemistry, and devices, and in support technologies including self-measurement and patient education. But unmet needs remain large. Today's therapy cannot deliver minute-to-minute control of glucose levels, and cannot imitate the reflex/incretin driven physiological insulin delivery at mealtimes. Further it depends on a raft of devices for administration several times a day, devices liked for their functionality, but disliked as an intrusive reminder of the condition, several times a day. Approaches to overcoming these barriers include closed-loop systems and further modification of insulin formulations, but are limited by fundamental underlying difficulties. While clinical studies of oral insulin are in progress, the barriers to success look daunting. Development of small-molecule approaches (insulin-mimetic tablets) appears to have stalled, while concepts for glucose-responsive insulin as yet fail to deliver the necessary insulin-to-glucose gradient. Gene therapy, feasible in animals in preliminary studies, is not capable of providing feedback control. Transplantation of cultured islets and islet B-cells from stem cells thus looks to the be the best long-term prospect for insulin delivery in terms of overcoming the above barriers, but is a true biotechnological tour-de-force which will take time to mature.

Emerging Treatment Strategies for Diabetes Mellitus and Associated Complications: An Update

The occurrence of diabetes mellitus (DM) is increasing rapidly at an accelerating rate worldwide. The status of diabetes has changed over the last three generations; whereas before it was deemed a minor disease of older people but currently it is now one of the leading causes of morbidity and mortality among middle-aged and young people. High blood glucose-mediated functional loss, insulin sensitivity, and insulin deficiency lead to chronic disorders such as Type 1 and Type 2 DM. Traditional treatments of DM, such as insulin sensitization and insulin secretion cause undesirable side effects, leading to patient incompliance and lack of treatment. Nanotechnology in diabetes studies has encouraged the development of new modalities for measuring glucose and supplying insulin that hold the potential to improve the quality of life of diabetics. Other therapies, such as β-cells regeneration and gene therapy, in addition to insulin and oral hypoglycemic drugs, are currently used to control diabetes. The present review highlights the nanocarrier-based drug delivery systems and emerging treatment strategies of DM.

From Mesenchymal Stromal/Stem Cells to Insulin-Producing Cells: Progress and Challenges

Mesenchymal stromal cells (MSCs) are an attractive option for cell therapy for type 1 diabetes mellitus (DM). These cells can be obtained from many sources, but bone marrow and adipose tissue are the most studied. MSCs have distinct advantages since they are nonteratogenic, nonimmunogenic and have immunomodulatory functions. Insulin-producing cells (IPCs) can be generated from MSCs by gene transfection, gene editing or directed differentiation. For directed differentiation, MSCs are usually cultured in a glucose-rich medium with various growth and activation factors. The resulting IPCs can control chemically-induced diabetes in immune-deficient mice. These findings are comparable to those obtained from pluripotent cells. PD-L₁ and PD-L₂ expression by MSCs is upregulated under inflammatory conditions. Immunomodulation occurs due to the interaction between these ligands and PD-1 receptors on T lymphocytes. If this function is maintained after differentiation, life-long immunosuppression or encapsulation could be avoided. In the clinical setting, two sites can be used for transplantation of IPCs: the subcutaneous tissue and the omentum. A 2-stage procedure is required for the former and a laparoscopic procedure for the latter. For either site, cells should be transplanted within a scaffold, preferably one from fibrin. Several questions remain unanswered. Will the transplanted cells be affected by the antibodies involved in the pathogenesis of type 1 DM? What is the functional longevity of these cells following their transplantation? These issues have to be addressed before clinical translation is attempted.

Graphical Abstract

Evaluation of fructosamine concentration as an index marker for glycaemic control in diabetic dogs

BACKGROUND

Although fructosamine is a commonly used surrogate marker to assess glycaemic control in diabetic dogs, its diagnostic accuracy has been questioned. The main objective of this study was to evaluate the reliability of fructosamine measurements to diagnose well and poorly controlled diabetes mellitus (DM), using continuous glucose monitoring as a gold standard.

METHODS

Twenty-four dogs with treated DM and continuous glucose monitoring for mean (±SD) 13.1 (±1.7) days were retrospectively analysed. Two assessment strategies were applied to categorize glycaemic control, and fructosamine concentrations were determined shortly after sensor cessation using a colorimetric assay.

RESULTS

Correlations of individual fructosamine concentrations with mean glucose as well as percentage of measurements > 15 mmol/L were not significant (p = 0.372, p = 0.129). Fructosamine did not differ between dogs with and without hypoglycaemic episodes (p = 0.64). Receiver operating characteristic analysis for fructosamine to diagnose either good or poor glycaemic control revealed AUC values of 0.71 (p = 0.025) indicating moderate accuracy, and 0.7 (p = 0.135) indicating AUC is non-discriminatory, respectively. The respective positive likelihood ratios for the optimal cutoffs to identify good (<396 μmol/L) and poor control (>449 μmol/L) were three.

CONCLUSIONS

Fructosamine measurement is an imperfect surrogate marker for classifying glycaemic control in diabetic dogs and can only complement serial glucose measurements.

Diagnosis and treatment of type 1 diabetes at the dawn of the personalized medicine era

Type 1 diabetes affects millions of people globally and requires careful management to avoid serious long-term complications, including heart and kidney disease, stroke, and loss of sight. The type 1 diabetes patient cohort is highly heterogeneous, with individuals presenting with disease at different stages and severities, arising from distinct etiologies, and overlaying varied genetic backgrounds. At present, the “one-size-fits-all” treatment for type 1 diabetes is exogenic insulin substitution therapy, but this approach fails to achieve optimal blood glucose control in many individuals. With advances in our understanding of early-stage diabetes development, diabetes stratification, and the role of genetics, type 1 diabetes is a promising candidate for a personalized medicine approach, which aims to apply “the right therapy at the right time, to the right patient”. In the case of type 1 diabetes, great efforts are now being focused on risk stratification for diabetes development to enable pre-clinical detection, and the application of treatments such as gene therapy, to prevent pancreatic destruction in a sub-set of patients. Alongside this, breakthroughs in stem cell therapies hold great promise for the regeneration of pancreatic tissues in some individuals. Here we review the recent initiatives in the field of personalized medicine for type 1 diabetes, including the latest discoveries in stem cell and gene therapy for the disease, and current obstacles that must be overcome before the dream of personalized medicine for all type 1 diabetes patients can be realized.

In Vivo Gene Therapy for Mucopolysaccharidosis Type III (Sanfilippo Syndrome): A New Treatment Horizon

For most lysosomal storage diseases (LSDs), there is no cure. Gene therapy is an attractive tool for treatment of LSDs caused by deficiencies in secretable lysosomal enzymes, in which neither full restoration of normal enzymatic activity nor transduction of all cells of the affected organ is necessary. However, some LSDs, such as mucopolysaccharidosis type III (MPSIII) diseases or Sanfilippo syndrome, represent a difficult challenge because patients suffer severe neurodegeneration with mild somatic alterations. The disease's main target is the central nervous system (CNS) and enzymes do not efficiently cross the blood-brain barrier (BBB) even if present at very high concentration in circulation. No specific treatment has been approved for MPSIII. In this study, we discuss the adeno-associated virus (AAV) vector-mediated gene transfer strategies currently being developed for MPSIII disease. These strategies rely on local delivery of AAV vectors to the CNS either through direct intraparenchymal injection at several sites or through delivery to the cerebrospinal fluid (CSF), which bathes the whole CNS, or exploit the properties of certain AAV serotypes capable of crossing the BBB upon systemic administration. Although studies in small and large animal models of MPSIII diseases have provided evidence supporting the efficacy and safety of all these strategies, there are considerable differences between the different routes of administration in terms of procedure-associated risks, vector dose requirements, sensitivity to the effect of circulating neutralizing antibodies that block AAV transduction, and potential toxicity. Ongoing clinical studies should shed light on which gene transfer strategy leads to highest clinical benefits while minimizing risks. The development of all these strategies opens a new horizon for treatment of not only MPSIII and other LSDs but also of a wide range of neurological diseases.

A Cure for Sanfilippo Syndrome? A Summary of Current Therapeutic Approaches and their Promise

Mucopolysaccharidoses III (MPS III, Sanfilippo syndrome) is a subtype of the Mucopolysaccharidoses (MPS), a group of inherited lysosomal disorders caused by a deficiency of lysosomal enzymes responsible for catabolizing glycosaminoglycans (GAGs). Although MPS III is rare, MPS diseases as a group are relatively frequent with an overall incidence of approximately 1 in 20,000 - 25,000 births. MPS III are paediatric diseases, which cause learning difficulties, behavioural disorders and dementia, as well as skeletal deformities and ultimately result in premature death. There are currently no approved treatments for MPS III, but a number of therapeutic approaches are under development. In the past 30 years, research using cellular and animal models have led to clinical trials involving enzyme replacement therapy (ERT), substrate reduction therapy (SRT) and gene therapy, while stem cells approaches remain at the pre-clinical stage. Although safety and clinical efficacy in animal models have shown promise, the results of clinical trials have proved costly and shown limited therapeutic effects. In this review, we describe the most recent results from clinical trials. While ERT and gene therapy are the most developed therapies for MPS III, we highlight the work that needs to be done to bring us closer to a real treatment for these devastating diseases.

Gene therapies for axonal neuropathies: Available strategies, successes to date, and what to target next

Nearly one-hundred loci in the human genome have been associated with different forms of Charcot-Marie-Tooth disease (CMT) and related inherited neuropathies. Despite this wealth of gene targets, treatment options are still extremely limited, and clear "druggable" pathways are not obvious for many of these mutations. However, recent advances in gene therapies are beginning to circumvent this challenge. Each type of CMT is a monogenic disorder, and the cellular targets are usually well-defined and typically include peripheral neurons or Schwann cells. In addition, the genetic mechanism is often also clear, with loss-of-function mutations requiring restoration of gene expression, and gain-of-function or dominant-negative mutations requiring silencing of the mutant allele. These factors combine to make CMT a good target for developing genetic therapies. Here we will review the state of relatively established gene therapy approaches, including viral vector-mediated gene replacement and antisense oligonucleotides for exon skipping, altering splicing, and gene knockdown. We will also describe earlier stage approaches for allele-specific knockdown and CRIPSR/Cas9 gene editing. We will next describe how these various approaches have been deployed in clinical and preclinical studies. Finally, we will evaluate various forms of CMT as candidates for gene therapy based on the current understanding of their genetics, cellular/tissue targets, validated animal models, and availability of patient populations and natural history data.

Anti-ageing gene therapy: Not so far away?

Improving healthspan is the main objective of anti-ageing research. Currently, innovative gene therapy-based approaches seem to be among the most promising for preventing and treating chronic polygenic pathologies, including age-related ones. The gene-based therapy allows to modulate the genome architecture using both direct (e.g., by gene editing) and indirect (e.g., by viral or non-viral vectors) approaches. Nevertheless, considering the extraordinary complexity of processes involved in ageing and ageing-related diseases, the effectiveness of these therapeutic options is often unsatisfactory and limited by their side-effects. Thus, clinical implementation of such applications is certainly a long-time process that will require many translation phases for addressing challenges. However, after overcoming these issues, their implementation in clinical practice may obviously provide new possibilities in anti-ageing medicine. Here, we review and discuss recent advances in this rapidly developing research field.

FGF21 gene therapy as treatment for obesity and insulin resistance

Prevalence of type 2 diabetes (T2D) and obesity is increasing worldwide. Currently available therapies are not suited for all patients in the heterogeneous obese/T2D population, hence the need for novel treatments. Fibroblast growth factor 21 (FGF21) is considered a promising therapeutic agent for T2D/obesity. Native FGF21 has, however, poor pharmacokinetic properties, making gene therapy an attractive strategy to achieve sustained circulating levels of this protein. Here, adeno-associated viral vectors (AAV) were used to genetically engineer liver, adipose tissue, or skeletal muscle to secrete FGF21. Treatment of animals under long-term high-fat diet feeding or of ob/ob mice resulted in marked reductions in body weight, adipose tissue hypertrophy and inflammation, hepatic steatosis, inflammation and fibrosis, and insulin resistance for > 1 year. This therapeutic effect was achieved in the absence of side effects despite continuously elevated serum FGF21. Furthermore, FGF21 overproduction in healthy animals fed a standard diet prevented the increase in weight and insulin resistance associated with aging. Our study underscores the potential of FGF21 gene therapy to treat obesity, insulin resistance, and T2D.

Five Years of Successful Inducible Transgene Expression Following Locoregional Adeno-Associated Virus Delivery in Nonhuman Primates with No Detectable Immunity

Anti-transgene immune responses elicited after intramuscular (i.m.) delivery of recombinant adeno-associated virus (rAAV) have been shown to hamper long-term transgene expression in large-animal models of rAAV-mediated gene transfer. To overcome this hurdle, an alternative mode of delivery of rAAV vectors in nonhuman primate muscles has been described: the locoregional (LR) intravenous route of administration. Using this injection mode, persistent inducible transgene expression for at least 1 year under the control of the tetracycline-inducible Tet-On system was previously reported in cynomolgus monkeys, with no immunity against the rtTA transgene product. The present study shows the long-term follow-up of these animals. It is reported that LR delivery of a rAAV2/1 vector allows long-term inducible expression up to at least 5 years post gene transfer, with no any detectable host immune response against the transactivator rtTA, despite its immunogenicity following i.m. gene transfer. This study shows for the first time a long-term regulation of muscle gene expression using a Tet-On-inducible system in a large-animal model. Moreover, these findings further confirm that the rAAV LR delivery route is efficient and immunologically safe, allowing long-term skeletal muscle gene transfer.

Type 1 and 2 diabetes mellitus: A review on current treatment approach and gene therapy as potential intervention

Type 1 and type 2 diabetes mellitus is a serious and lifelong condition commonly characterised by abnormally elevated blood glucose levels due to a failure in insulin production or a decrease in insulin sensitivity and function. Over the years, prevalence of diabetes has increased globally and it is classified as one of the leading cause of high mortality and morbidity rate. Furthermore, diabetes confers a huge economic burden due to its management costs as well as its complications are skyrocketing. The conventional medications in diabetes treatment focusing on insulin secretion and insulin sensitisation cause unwanted side effects to patients and lead to incompliance as well as treatment failure. Besides insulin and oral hypoglycaemic agents, other treatments such as gene therapy and induced β-cells regeneration have not been widely introduced to manage diabetes. Therefore, this review aims to deliver an overview of the current conventional medications in diabetes, discovery of newer pharmacological drugs and gene therapy as a potential intervention of diabetes in the future.

Codon-Optimization of Wild-Type Adeno-Associated Virus Capsid Sequences Enhances DNA Family Shuffling while Conserving Functionality

Adeno-associated virus (AAV) vectors have become one of the most widely used gene transfer tools in human gene therapy. Considerable effort is currently being focused on AAV capsid engineering strategies with the aim of developing novel variants with enhanced tropism for specific human cell types, decreased human seroreactivity, and increased manufacturability. Selection strategies based on directed evolution rely on the generation of highly variable AAV capsid libraries using methods such as DNA-family shuffling, a technique reliant on stretches of high DNA sequence identity between input parental capsid sequences. This identity dependence for reassembly of shuffled capsids is inherently limiting and results in decreased shuffling efficiency as the phylogenetic distance between parental AAV capsids increases. To overcome this limitation, we have developed a novel codon-optimization algorithm that exploits evolutionarily defined codon usage at each amino acid residue in the parental sequences. This method increases average sequence identity between capsids, while enhancing the probability of retaining capsid functionality, and facilitates incorporation of phylogenetically distant serotypes into the DNA-shuffled libraries. This technology will help accelerate the discovery of an increasingly powerful repertoire of AAV capsid variants for cell-type and disease-specific applications.

Proinsulin protects against age-related cognitive loss through anti-inflammatory convergent pathways

Brain inflammaging is increasingly considered as contributing to age-related cognitive loss and neurodegeneration. Despite intensive research in multiple models, no clinically effective pharmacological treatment has been found yet. Here, in the mouse model of brain senescence SAMP8, we tested the effects of proinsulin, a promising neuroprotective agent that was previously proven to be effective in mouse models of retinal neurodegeneration. Proinsulin is the precursor of the hormone insulin but also upholds developmental physiological effects, particularly as a survival factor for neural cells. Adeno-associated viral vectors of serotype 1 bearing the human proinsulin gene were administered intramuscularly to obtain a sustained release of proinsulin into the blood stream, which was able to reach the target area of the hippocampus. SAMP8 mice and the control strain SAMR1 were treated at 1 month of age. At 6 months, behavioral testing exhibited cognitive loss in SAMP8 mice treated with the null vector. Remarkably, the cognitive performance achieved in spatial and recognition tasks by SAMP8 mice treated with proinsulin was similar to that of SAMR1 mice. In the hippocampus, proinsulin induced the activation of neuroprotective pathways and the downstream signaling cascade, leading to the decrease of neuroinflammatory markers. Furthermore, the decrease of astrocyte reactivity was a central effect, as demonstrated in the connectome network of changes induced by proinsulin. Therefore, the neuroprotective effects of human proinsulin unveil a new pharmacological potential therapy in the fight against cognitive loss in the elderly.