Present and future cell therapies for pancreatic beta cell replenishment

Expression of Pfkfb isoenzymes during in vitro differentiation of mouse embryonic stem cells into insulin-producing cells

Background/aim

Type 1 diabetes mellitus (T1DM) is caused by the autoimmune-mediated destruction of insulin-producing cells (IPCs) and still has no effective cure. Better understanding of the molecular mechanisms involved in the differentiation of embryonic stem cells (ESCs) into IPCs may help us improve the therapeutic strategies for treating T1DM. 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (Pfkfb1-4) are key regulators of glucose metabolism. Although Pfkfb3 has been shown to be required for the growth of early differentiated mouse ESCs (mESCs), more studies are needed to further assess the roles of Pfkfb isoenzymes in embryonic development and differentiation, particularly into specific cell types. In this study, we aimed to elucidate the changes in the expression of Pfkfb isoenzymes on the differentiation of mESCs into IPCs.

Materials and methods

A 3-step protocol was used to differentiate R1 and J1 mESCs into IPCs. The changes in the gene expression of MafA, MafB, Ins2, and Nkx6.1 (IPC specific markers) and Pfkfb1-4 were analyzed using real-time quantitative polymerase chain reaction (qPCR). Insulin expression and secretion were determined by immunofluorescence (IF) staining and the enzyme linked immunosorbent assay (ELISA), respectively.

Results

Upon differentiation, the IPC specific markers in differentiated cells were upregulated. Continued differentiation was confirmed by the development of insulin-positive islet-like clusters that secreted insulin in response to glucose uptake. Expressions of the Pfkfb2 and Pfkfb3 isoenzymes were markedly increased in various stages of differentiation.

Conclusion

These findings suggest that Pfkfb2 and Pfkfb3 may impact the differentiation of mESCs into IPCs and the regulation of the insulin response to glucose levels. This study also lays a foundation for researchers to further probe the roles of Pfkfb isoenzymes on the differentiation of mESCs into IPCs and may open new avenues for regenerative medicine.

FasL microgels induce immune acceptance of islet allografts in nonhuman primates

Islet transplantation to treat insulin-dependent diabetes is greatly limited by the need for maintenance immunosuppression. We report a strategy through which cotransplantation of allogeneic islets and streptavidin (SA)-FasL-presenting microgels to the omentum under transient rapamycin monotherapy resulted in robust glycemic control, sustained C-peptide levels, and graft survival in diabetic nonhuman primates for >6 months. Surgical extraction of the graft resulted in prompt hyperglycemia. In contrast, animals receiving microgels without SA-FasL under the same rapamycin regimen rejected islet grafts acutely. Graft survival was associated with increased number of FoxP3+ cells in the graft site with no significant changes in T cell systemic frequencies or responses to donor and third-party antigens, indicating localized tolerance. Recipients of SA-FasL microgels exhibited normal liver and kidney metabolic function, demonstrating safety. This localized immunomodulatory strategy succeeded with unmodified islets and does not require long-term immunosuppression, showing translational potential in β cell replacement for treating type 1 diabetes.

Delivery of therapeutic agents and cells to pancreatic islets: Towards a new era in the treatment of diabetes

Pancreatic islet cells, and in particular insulin-producing beta cells, are centrally involved in the pathogenesis of diabetes mellitus. These cells are of paramount importance for the endocrine control of glycemia and glucose metabolism. In Type 1 Diabetes, islet beta cells are lost due to an autoimmune attack. In Type 2 Diabetes, beta cells become dysfunctional and insufficient to counterbalance insulin resistance in peripheral tissues. Therapeutic agents have been developed to support the function of islet cells, as well as to inhibit deleterious immune responses and inflammation. Most of these agents have undesired effects due to systemic administration and off-target effects. Typically, only a small fraction of therapeutic agent reaches the desired niche in the pancreas. Because islets and their beta cells are scattered throughout the pancreas, access to the niche is limited. Targeted delivery to pancreatic islets could dramatically improve the therapeutic effect, lower the dose requirements, and lower the side effects of agents administered systemically. Targeted delivery is especially relevant for those therapeutics for which the manufacturing is difficult and costly, such as cells, exosomes, and microvesicles. Along with therapeutic agents, imaging reagents intended to quantify the beta cell mass could benefit from targeted delivery. Several methods have been developed to improve the delivery of agents to pancreatic islets. Intra-arterial administration in the pancreatic artery is a promising surgical approach, but it has inherent risks. Targeted delivery strategies have been developed based on ligands for cell surface molecules specific to islet cells or inflamed vascular endothelial cells. Delivery methods range from nanocarriers and vectors to deliver pharmacological agents to viral and non-viral vectors for the delivery of genetic constructs. Several strategies demonstrated enhanced therapeutic effects in diabetes with lower amounts of therapeutic agents and lower off-target side effects. Microvesicles, exosomes, polymer-based vectors, and nanocarriers are gaining popularity for targeted delivery. Notably, liposomes, lipid-assisted nanocarriers, and cationic polymers can be bioengineered to be immune-evasive, and their advantages to transport cargos into target cells make them appealing for pancreatic islet-targeted delivery. Viral vectors have become prominent tools for targeted gene delivery. In this review, we discuss the latest strategies for targeted delivery of therapeutic agents and imaging reagents to pancreatic islet cells.

The Current Status of Bioartificial Pancreas Devices

Type 1 diabetes mellitus is a common and highly morbid disease for which there is no cure. Treatment primarily involves exogenous insulin administration, and, under specific circumstances, islet or pancreas transplantation. However, insulin replacement alone fails to replicate the endocrine function of the pancreas and does not provide durable euglycemia. In addition, transplantation requires lifelong use of immunosuppressive medications, which has deleterious side effects, is expensive, and is inappropriate for use in adolescents. A bioartificial pancreas that provides total endocrine pancreatic function without immunosuppression is a potential therapy for treatment of type 1 diabetes. Numerous models are in development and take different approaches to cell source, encapsulation method, and device implantation location. We review current therapies for type 1 diabetes mellitus, the requirements for a bioartificial pancreas, and quantitatively compare device function.

Enhancing islet transplantation using a biocompatible collagen-PDMS bioscaffold enriched with dexamethasone-microplates

Islet transplantation is a promising approach to enable type 1 diabetic patients to attain glycemic control independent of insulin injections. However, up to 60% of islets are lost immediately following transplantation. To improve this outcome, islets can be transplanted within bioscaffolds, however, synthetic bioscaffolds induce an intense inflammatory reaction which can have detrimental effects on islet function and survival. In the present study, we first improved the biocompatibility of polydimethylsiloxane (PDMS) bioscaffolds by coating them with collagen. To reduce the inflammatory response to PDMS bioscaffolds, we then enriched the bioscaffolds with dexamethasone-loaded microplates (DEX-µScaffolds). These DEX-microplates have the ability to release DEX in a sustained manner over 7 weeks within a therapeutic range that does not affect the glucose responsiveness of the islets but which minimizes inflammation in the surrounding microenvironment. The bioscaffold showed excellent mechanical properties that enabled it to resist pore collapse thereby helping to facilitate islet seeding and its handling for implantation, and subsequent engraftment, within the epididymal fat pad (EFP). Following the transplantation of islets into the EFP of diabetic mice using DEX-µScaffolds there was a return in basal blood glucose to normal values by day 4, with normoglycemia maintained for 30 days. Furthermore, these animals demonstrated a normal dynamic response to glucose challenges with histological evidence showing reduced pro-inflammatory cytokines and fibrotic tissue surrounding DEX-µScaffolds at the transplantation site. In contrast, diabetic animals transplanted with either islets alone or islets in bioscaffolds without DEX microplates were not able to regain glycemic control during basal conditions with overall poor islet function. Taken together, our data show that coating PDMS bioscaffolds with collagen, and enriching them with DEX-microplates, significantly prolongs and enhances islet function and survival.

Improving the Function and Engraftment of Transplanted Pancreatic Islets Using Pulsed Focused Ultrasound Therapy

This study demonstrates that pulsed focused ultrasound (pFUS) therapy can non-invasively enhance the function and engraftment of pancreatic islets following transplantation. In vitro, we show that islets treated with pFUS at low (peak negative pressure (PNP): 106kPa, spatial peak temporal peak intensity (I_sptp): 0.71 W/cm²), medium (PNP: 150kPa, I_sptp: 1.43 W/cm²) or high (PNP: 212kPa, I_sptp: 2.86 W/cm²) acoustic intensities were stimulated resulting in an increase in their function (i.e. insulin secretion at low-intensity: 1.15 ± 0.17, medium-intensity: 2.02 ± 0.25, and high-intensity: 2.54 ± 0.38 fold increase when compared to control untreated islets; P < 0.05). Furthermore, we have shown that this improvement in islet function is a result of pFUS increasing the intracellular concentration of calcium (Ca²⁺) within islets which was also linked to pFUS increasing the resting membrane potential (V_m) of islets. Following syngeneic renal sub-capsule islet transplantation in C57/B6 mice, pFUS (PNP: 2.9 MPa, I_sptp: 895 W/cm²) improved the function of transplanted islets with diabetic animals rapidly re-establishing glycemic control. In addition, pFUS was able to enhance the engraftment by facilitating islet revascularization and reducing inflammation. Given a significant number of islets are lost immediately following transplantation, pFUS has the potential to be used in humans as a novel non-invasive therapy to facilitate islet function and engraftment, thereby improving the outcome of diabetic patients undergoing islet transplantation.

FGF-2b and h-PL Transform Duct and Non-Endocrine Human Pancreatic Cells into Endocrine Insulin Secreting Cells by Modulating Differentiating Genes

Background: Diabetes mellitus (DM) is a multifactorial disease orphan of a cure. Regenerative medicine has been proposed as novel strategy for DM therapy. Human fibroblast growth factor (FGF)-2b controls β-cell clusters via autocrine action, and human placental lactogen (hPL)-A increases functional β-cells. We hypothesized whether FGF-2b/hPL-A treatment induces β-cell differentiation from ductal/non-endocrine precursor(s) by modulating specific genes expression. Methods: Human pancreatic ductal-cells (PANC-1) and non-endocrine pancreatic cells were treated with FGF-2b plus hPL-A at 500 ng/mL. Cytofluorimetry and Immunofluorescence have been performed to detect expression of endocrine, ductal and acinar markers. Bromodeoxyuridine incorporation and annexin-V quantified cells proliferation and apoptosis. Insulin secretion was assessed by RIA kit, and electron microscopy analyzed islet-like clusters. Results: Increase in PANC-1 duct cells de-differentiation into islet-like aggregates was observed after FGF-2b/hPL-A treatment showing ultrastructure typical of islets-aggregates. These clusters, after stimulation with FGF-2b/hPL-A, had significant (p < 0.05) increase in insulin, C-peptide, pancreatic and duodenal homeobox 1 (PDX-1), Nkx2.2, Nkx6.1, somatostatin, glucagon, and glucose transporter 2 (Glut-2), compared with control cells. Markers of PANC-1 (Cytokeratin-19, MUC-1, CA19-9) were decreased (p < 0.05). These aggregates after treatment with FGF-2b/hPL-A significantly reduced levels of apoptosis. Conclusions: FGF-2b and hPL-A are promising candidates for regenerative therapy in DM by inducing de-differentiation of stem cells modulating pivotal endocrine genes.

Cell therapies for pancreatic beta-cell replenishment

The current treatment approach for type 1 diabetes is based on daily insulin injections, combined with blood glucose monitoring. However, administration of exogenous insulin fails to mimic the physiological activity of the islet, therefore diabetes often progresses with the development of serious complications such as kidney failure, retinopathy and vascular disease. Whole pancreas transplantation is associated with risks of major invasive surgery along with side effects of immunosuppressive therapy to avoid organ rejection. Replacement of pancreatic beta-cells would represent an ideal treatment that could overcome the above mentioned therapeutic hurdles. In this context, transplantation of islets of Langerhans is considered a less invasive procedure although long-term outcomes showed that only 10 % of the patients remained insulin independent five years after the transplant. Moreover, due to shortage of organs and the inability of islet to be expanded ex vivo, this therapy can be offered to a very limited number of patients. Over the past decade, cellular therapies have emerged as the new frontier of treatment of several diseases. Furthermore the advent of stem cells as renewable source of cell-substitutes to replenish the beta cell population, has blurred the hype on islet transplantation. Breakthrough cellular approaches aim to generate stem-cell-derived insulin producing cells, which could make diabetes cellular therapy available to millions. However, to date, stem cell therapy for diabetes is still in its early experimental stages. This review describes the most reliable sources of stem cells that have been developed to produce insulin and their most relevant experimental applications for the cure of diabetes.

Mesenchymal stem cells in the treatment of type 1 diabetes mellitus

Diabetes mellitus type 1 is a form of diabetes mellitus that results from the autoimmune destruction of insulin-producing beta cells in the pancreas. The current gold standard therapy for pancreas transplantation has limitations because of the long list of waiting patients and the limited supply of donor pancreas. Mesenchymal stem cells (MSCs), a relatively new potential therapy in various fields, have already made their mark in the young field of regenerative medicine. Recent studies have shown that the implantation of MSCs decreases glucose levels through paracrine influences rather than through direct transdifferentiation into insulin-producing cells. Therefore, these cells may use pro-angiogenic and immunomodulatory effects to control diabetes following the cotransplantation with pancreatic islets. In this review, we present and discuss new approaches of using MSCs in the treatment of diabetes mellitus type 1.

The levels of circulating TRAIL at the onset of type 1 diabetes are markedly decreased in patients with ketoacidosis and with the highest insulin requirement

Experimental evidence in animal models suggests that TNF-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily, might play an important role in type 1 diabetes (T1D). We have performed a retrospective study by analyzing the sera of a cohort of pediatric subjects (age ≤18 years; n = 507) consisting of (1) patients diagnosed with T1D (n = 387), (2) healthy individuals (n = 98, considered as controls), and (3) healthy autoantibody-positive subjects (n = 22). Patients with T1D exhibited significantly decreased levels of circulating TRAIL with respect to the control healthy subjects, as well as to the healthy autoantibody-positive subjects. Within the T1D group, no differences in the levels of circulating TRAIL were observed between patients with or without other concomitant autoimmune pathologies. Of note, the levels of TRAIL were significantly lower in the T1D patients analyzed at onset, although reduction in TRAIL levels persisted also in patients analyzed after disease onset (>1 year from diagnosis). In particular, T1D patients who exhibited ketoacidosis at onset showed significantly lower levels of circulating TRAIL with respect to patients without ketoacidosis at onset. Moreover, the levels of TRAIL at diagnosis correlated inversely with the insulin requirement up to 21 months of follow-up. This is the first study demonstrating that the levels of circulating TRAIL are significantly decreased in T1D, with the lowest levels of TRAIL being observed in patients with ketoacidosis at the onset and with the highest insulin requirement.

Beta cell dynamics: beta cell replenishment, beta cell compensation and diabetes

Type 2 diabetes, characterized by persistent hyperglycemia, arises mostly from beta cell dysfunction and insulin resistance and remains a highly complex metabolic disease due to various stages in its pathogenesis. Glucose homeostasis is primarily regulated by insulin secretion from the beta cells in response to prevailing glycemia. Beta cell populations are dynamic as they respond to fluctuating insulin demand. Beta cell replenishment and death primarily regulate beta cell populations. Beta cells, pancreatic cells, and extra-pancreatic cells represent the three tiers for replenishing beta cells. In rodents, beta cell self-replenishment appears to be the dominant source for new beta cells supported by pancreatic cells (non-beta islet cells, acinar cells, and duct cells) and extra-pancreatic cells (liver, neural, and stem/progenitor cells). In humans, beta cell neogenesis from non-beta cells appears to be the dominant source of beta cell replenishment as limited beta cell self-replenishment occurs particularly in adulthood. Metabolic states of increased insulin demand trigger increased insulin synthesis and secretion from beta cells. Beta cells, therefore, adapt to support their physiology. Maintaining physiological beta cell populations is a strategy for targeting metabolic states of persistently increased insulin demand as in diabetes.

Regenerative medicine technology applied to gastroenterology: Current status and future perspectives

This special issue of World Journal of Gastroenterology has been conceived to illustrate to gastroenterology operators the role that regenerative medicine (RM) will have in the progress of gastrointestinal (GI) medicine. RM is a multidisciplinary field aiming to replace, regenerate or repair diseased tissues or organs. The past decade has been marked by numerous ground-breaking achievements that led experts in the field to manufacture functional substitutes of relatively simple organs. This progress is paving the ground for investigations that aims to the bioengineering and regeneration of more complex organs like livers, pancreas and intestine. In this special issue, the reader will be introduced, hand-in-hand, to explore the field of RM and will be educated on the progress, pitfalls and promise of RM technologies as applied to GI medicine.