Advancements in transplantation therapy for diabetes: Pancreas, islet and stem cell

Emerging diabetes therapies: Regenerating pancreatic β cells

The incidence of diabetes mellitus (DM) is steadily increasing annually, with 537 million diabetic patients as of 2021. Restoring diminished β cell mass or impaired islet function is crucial in treating DM, particularly type 1 diabetes mellitus (T1DM). However, the regenerative capacity of islet β cells, which primarily produce insulin, is severely limited, and natural regeneration is only observed in young rodents or children. Hence, there is an urgent need to develop advanced therapeutic approaches that can regenerate endogenous β cells or replace them with stem cell (SC)-derived or engineered β-like cells. Current strategies for treating insulin-dependent DM mainly include promoting the self-replication of endogenous β cells, inducing SC differentiation, reprogramming non-β cells into β-like cells, and generating pancreatic-like organoids through cell-based intervention. In this Review, we discuss the current state of the art in these approaches, describe associated challenges, propose potential solutions, and highlight ongoing efforts to optimize β cell or islet transplantation and related clinical trials. These effective cell-based therapies will generate a sustainable source of functional β cells for transplantation and lay strong foundations for future curative treatments for DM.

Diabetes current and future translatable therapies

Diabetes is one of the major diseases and concerns of public health systems that affects over 200 million patients worldwide. It is estimated that 90% of these patients suffer from diabetes type 2, while 10% present diabetes type 1. This type of diabetes and certain types of diabetes type 2, are characterized by dysregulation of blood glycemic levels due to the total or partial depletion of insulin-secreting pancreatic β-cells. Different approaches have been proposed for long-term treatment of insulin-dependent patients; amongst them, cell-based approaches have been the subject of basic and clinical research since they allow blood glucose level sensing and in situ insulin secretion. The current gold standard for insulin-dependent patients is on-demand exogenous insulin application; cell-based therapies aim to remove this burden from the patient and caregivers. In recent years, protocols to isolate and implant pancreatic islets from diseased donors have been developed and tested in clinical trials. Nevertheless, the shortage of donors, along with the need of immunosuppressive companion therapies, have pushed researchers to focus their attention and efforts to overcome these disadvantages and develop alternative strategies. This review discusses current tested clinical approaches and future potential alternatives for diabetes type 1, and some diabetes type 2, insulin-dependent patients. Additionally, advantages and disadvantages of these discussed methods.

Regeneration of Pancreatic Cells Using Optimized Nanoparticles and l-Glutamic Acid-Gelatin Scaffolds with Controlled Topography and Grafted Activin A/BMP4

Regeneration of insulin-producing cells (IPCs) from induced pluripotent stem cells (iPSCs) under controlled conditions has a lot of promise to emulate the pancreatic mechanism in vivo as a foundation of cell-based diabetic therapy. l-Glutamic acid-gelatin scaffolds with orderly pore sizes of 160 and 200 μm were grafted with activin A and bone morphogenic proteins 4 (BMP4) to differentiate iPSCs into definitive endoderm (DE) cells, which were then guided with fibroblast growth factor 7 (FGF7)-grafted retinoic acid (RA)-loaded solid lipid nanoparticles (FR-SLNs) to harvest IPCs. Response surface methodology was adopted to optimize the l-glutamic acid-to-gelatin ratio of scaffolds and to optimize surfactant concentration and lipid proportion in FR-SLNs. Experimental results of immunofluorescence, flow cytometry, and western blots revealed that activin A (100 ng/mL)-BMP4 (50 ng/mL)-l-glutamic acid (5%)-gelatin (95%) scaffolds provoked the largest number of SOX17-positive DE cells from iPSCs. Treatment with FGF7 (50 ng/mL)-RA (600 ng/mL)-SLNs elicited the highest number of PDX1-positive β-cells from differentiated DE cells. To imitate the natural pancreas, the scaffolds with controlled topography were appropriate for IPC production with sufficient insulin secretion. Hence, the current scheme using FR-SLNs and activin A-BMP4-l-glutamic acid-gelatin scaffolds in the two-stage differentiation of iPSCs can be promising for replacing impaired β-cells in diabetic management.

Noninvasive quantitative evaluation of viable islet grafts using 111 In-exendin-4 SPECT/CT

Islet transplantation (IT) is an effective β-cell replacement therapy for patients with type 1 diabetes; however, the lack of methods to detect islet grafts and evaluate their β-cell mass (BCM) has limited the further optimization of IT protocols. Therefore, the development of noninvasive β-cell imaging is required. In this study, we investigated the utility of the ¹¹¹ Indium-labeled exendin-4 probe {[Lys12(111In-BnDTPA-Ahx)] exendin-4} (¹¹¹ In exendin-4) to evaluate islet graft BCM after intraportal IT. The probe was cultured with various numbers of isolated islets. Streptozotocin-induced diabetic mice were intraportally transplanted with 150 or 400 syngeneic islets. After a 6-week observation following IT, the ex-vivo liver graft uptake of ¹¹¹ In-exendin-4 was compared with the liver insulin content. In addition, the in-vivo liver graft uptake of ¹¹¹ In exendin-4 using SPECT/CT was compared with that of liver graft BCM measured by a histological method. As a result, probe accumulation was significantly correlated with islet numbers. The ex-vivo liver graft uptake in the 400-islet-transplanted group was significantly higher than that in the control and the 150-islet-transplanted groups, consistent with glycemic control and liver insulin content. In conclusion, in-vivo SPECT/CT displayed liver islet grafts, and uptakes were corroborated by histological liver BCM. ¹¹¹ In-exendin-4 SPECT/CT can be used to visualize and evaluate liver islet grafts noninvasively after intraportal IT.

Advances in insulin therapy from discovery to β-cell replacement

Insulin therapy using insulin purified from porcine or bovine pancreas revolutionized diabetes therapy in the 1920s. A series of advances including cloning human insulin cDNA enabled the development of recombinant human insulin with improved features. Insulin treatment for diabetes may well be upended by β-cell replacement therapy in the coming decades.

A unique profile of insulin antibody titer in islet-transplanted patients

Insulin antibodies (IAs) can cause glycemic variability. Islet transplantation (ITx) is a treatment for insulin‐deficient diabetes that aims to establish on‐target glycemic control in the absence of hypoglycemia. To date, there has not been a detailed case study of the association between ITx and IA levels. In this study, we identified a unique profile of IA titers, which differed from glutamic acid decarboxylase antibody titers, in four ITx patients. IA levels decreased with intensified immunosuppressive therapy, whereas glutamic acid decarboxylase antibodies increased transiently after ITx. These data suggest the possibility that IAs, unlike other islet autoantibodies, were eliminated due to immunosuppression after transplantation therapy. The disappearance of IAs, as well as the restoration of regulated insulin secretion after ITx, might have a positive effect on glycemic control in recipients with diabetes. Furthermore, this unique feature is suggestive of immunological pathogenesis and has implications for the treatment of IA‐causing disease conditions.

Non-invasive Beta-cell Imaging: Visualization, Quantification, and Beyond

Pancreatic beta (β)-cell dysfunction and reduced mass play a central role in the development and progression of diabetes mellitus. Conventional histological β-cell mass (BCM) analysis is invasive and limited to cross-sectional observations in a restricted sampling area. However, the non-invasive evaluation of BCM remains elusive, and practical in vivo and clinical techniques for β-cell-specific imaging are yet to be established. The lack of such techniques hampers a deeper understanding of the pathophysiological role of BCM in diabetes, the implementation of personalized BCM-based diabetes management, and the development of antidiabetic therapies targeting BCM preservation and restoration. Nuclear medical techniques have recently triggered a major leap in this field. In particular, radioisotope-labeled probes using exendin peptides that include glucagon-like peptide-1 receptor (GLP-1R) agonist and antagonist have been employed in positron emission tomography and single-photon emission computed tomography. These probes have demonstrated high specificity to β cells and provide clear images accurately showing uptake in the pancreas and transplanted islets in preclinical in vivo and clinical studies. One of these probes, ¹¹¹indium-labeled exendin-4 derivative ([Lys¹²(¹¹¹In-BnDTPA-Ahx)]exendin-4), has captured the longitudinal changes in BCM during the development and progression of diabetes and under antidiabetic therapies in various mouse models of type 1 and type 2 diabetes mellitus. GLP-1R-targeted imaging is therefore a promising tool for non-invasive BCM evaluation. This review focuses on recent advances in non-invasive in vivo β-cell imaging for BCM evaluation in the field of diabetes; in particular, the exendin-based GLP-1R-targeted nuclear medicine techniques.