Pancreatic β-cell imaging in humans: fiction or option?

Zinc-chelating BET bromodomain inhibitors equally target islet endocrine cell types

Inhibition of the bromodomain and extraterminal domain (BET) protein family is a potential strategy to prevent and treat diabetes; however, the clinical use of BET bromodomain inhibitors (BETis) is associated with adverse effects. Here, we explore a strategy for targeting BETis to β cells by exploiting the high-zinc (Zn2+) concentration in β cells relative to other cell types. We report the synthesis of a novel, Zn2+-chelating derivative of the pan-BETi (+)-JQ1, (+)-JQ1-DPA, in which (+)-JQ1 was conjugated to dipicolyl amine (DPA). As controls, we synthesized (+)-JQ1-DBA, a non-Zn2+-chelating derivative, and (-)-JQ1-DPA, an inactive enantiomer that chelates Zn2+. Molecular modeling and biophysical assays showed that (+)-JQ1-DPA and (+)-JQ1-DBA retain potent binding to BET bromodomains in vitro. Cellular assays demonstrated (+)-JQ1-DPA attenuated NF-ĸB target gene expression in β cells stimulated with the proinflammatory cytokine interleukin 1β. To assess β-cell selectivity, we isolated islets from a mouse model that expresses green fluorescent protein in insulin-positive β cells and mTomato in insulin-negative cells (non-β cells). Surprisingly, Zn2+ chelation did not confer β-cell selectivity as (+)-JQ1-DPA was equally effective in both β and α cells; however, (+)-JQ1-DPA was less effective in macrophages, a nonendocrine islet cell type. Intriguingly, the non-Zn2+-chelating derivative (+)-JQ1-DBA displayed the opposite selectivity, with greater effect in macrophages compared with (+)-JQ1-DPA, suggesting potential as a macrophage-targeting molecule. These findings suggest that Zn2+-chelating small molecules confer endocrine cell selectivity rather than β-cell selectivity in pancreatic islets and provide valuable insights and techniques to assess Zn2+ chelation as an approach to selectively target small molecules to pancreatic β cells.NEW & NOTEWORTHY Inhibition of BET bromodomains is a novel potential strategy to prevent and treat diabetes mellitus. However, BET inhibitors have negative side effects. We synthesized a BET inhibitor expected to exploit the high zinc concentration in β cells to accumulate in β cells. We show our inhibitor targeted pancreatic endocrine cells; however, it was less effective in immune cells. A control inhibitor showed the opposite effect. These findings help us understand how to target specific cells in diabetes treatment.

New Insights and Potential Therapeutic Interventions in Metabolic Diseases

Endocrine homeostasis and metabolic diseases have been the subject of extensive research in recent years. The development of new techniques and insights has led to a deeper understanding of the mechanisms underlying these conditions and opened up new avenues for diagnosis and treatment. In this review, we discussed the rise of metabolic diseases, especially in Western countries, the genetical, psychological, and behavioral basis of metabolic diseases, the role of nutrition and physical activity in the development of metabolic diseases, the role of single-cell transcriptomics, gut microbiota, epigenetics, advanced imaging techniques, and cell-based therapies in metabolic diseases. Finally, practical applications derived from this information are made.

Advances of functional nanomaterials for magnetic resonance imaging and biomedical engineering applications

Functional nanomaterials have been widely used in biomedical fields due to their good biocompatibility, excellent physicochemical properties, easy surface modification, and easy regulation of size and morphology. Functional nanomaterials for magnetic resonance imaging (MRI) can target specific sites in vivo and more easily detect disease-related specific biomarkers at the molecular and cellular levels than traditional contrast agents, achieving a broad application prospect in MRI. This review focuses on the basic principles of MRI, the classification, synthesis and surface modification methods of contrast agents, and their clinical applications to provide guidance for designing novel contrast agents and optimizing the contrast effect. Furthermore, the latest biomedical advances of functional nanomaterials in medical diagnosis and disease detection, disease treatment, the combination of diagnosis and treatment (theranostics), multi-model imaging and nanozyme are also summarized and discussed. Finally, the bright application prospects of functional nanomaterials in biomedicine are emphasized and the urgent need to achieve significant breakthroughs in the industrial transformation and the clinical translation is proposed. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Intravital imaging of islet Ca2+ dynamics reveals enhanced β cell connectivity after bariatric surgery in mice

Bariatric surgery improves both insulin sensitivity and secretion and can induce diabetes remission. However, the mechanisms and time courses of these changes, particularly the impact on β cell function, are difficult to monitor directly. In this study, we investigated the effect of Vertical Sleeve Gastrectomy (VSG) on β cell function in vivo by imaging Ca²⁺ dynamics in islets engrafted into the anterior eye chamber. Mirroring its clinical utility, VSG in mice results in significantly improved glucose tolerance, and enhanced insulin secretion. We reveal that these benefits are underpinned by augmented β cell function and coordinated activity across the islet. These effects involve changes in circulating GLP-1 levels which may act both directly and indirectly on the β cell, in the latter case through changes in body weight. Thus, bariatric surgery leads to time-dependent increases in β cell function and intra-islet connectivity which are likely to contribute to diabetes remission.

Glucagon-like Peptide-1 Receptor as Emerging Target: Will It Make It to the Clinic?

The glucagon-like peptide-1 receptor (GLP-1R) is an emerging target due to its high expression in benign insulinomas as well as in islet cell hypertrophia/hyperplasia (nesidioblastosis) and pancreatic β-cells. In 2008, occult insulinomas were localized for the first time in men using the metabolically stable radiolabeled glucagon-like peptide-1 (GLP-1) agonist [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 (111In-DTPA-exendin-4). Afterward, several radiopharmaceuticals for GLP-1R PET/CT imaging were synthesized and evaluated, for example, [Nle14,Lys40(Ahx-DOTA-68Ga)NH2]-exendin-4 (68Ga-DOTA-exendin-4), [Cys40(MAL-NOTA-68Ga)NH2]-exendin-4 (68Ga-NOTA-exendin-4), and [Lys40(NODAGA-68Ga)NH2]-exendin-4 (68Ga-NODAGA-exendin-4). Several prospective comparison studies provided evidence that GLP-1R PET/CT is significantly more sensitive than contrast-enhanced MRI (ceMRI), contrast-enhanced CT (ceCT), GLP-1R SPECT/CT, somatostatin receptor PET/CT, and SPECT/CT in the detection of benign insulinomas, and insulinomas in the context of multiple endocrine neoplasia type 1. As a result, the European Neuroendocrine Tumor Society guidelines recommend GLP-1R imaging or selective intraarterial calcium stimulation and venous sampling (ASVS) in patients for whom there is a clinical suspicion of having an insulinoma but who have a negative ceMRI/ceCT or negative endoscopic ultrasound. Furthermore, there is growing evidence that GLP-1R PET/CT can visualize and localize adult nesidioblastosis. This is clinically relevant as the distinction between focal and diffuse nesidioblastosis is critical in directing a therapeutic strategy in these patients. Prospective studies have proven the clinical relevance of GLP-1R imaging as it is often the only imaging modality able to localize the insulinoma or nesidioblastosis. It is therefore likely that this noninvasive imaging modality will replace the invasive localization of insulinomas using ASVS. More experimental indications for GLP-1R imaging include the diagnosis of an insulinoma/nesidioblastosis in patients with postprandial hypoglycemia after bariatric bypass surgery and monitoring β-cells in patients with brittle type 1 diabetes after islet-cell transplantation. We believe that these indications and possibly future indications will bring GLP-1R imaging to the clinic.

Islet Regeneration: Endogenous and Exogenous Approaches

Both type 1 and type 2 diabetes are characterized by a progressive loss of beta cell mass that contributes to impaired glucose homeostasis. Although an optimal treatment option would be to simply replace the lost cells, it is now well established that unlike many other organs, the adult pancreas has limited regenerative potential. For this reason, significant research efforts are focusing on methods to induce beta cell proliferation (replication of existing beta cells), promote beta cell formation from alternative endogenous cell sources (neogenesis), and/or generate beta cells from pluripotent stem cells. In this article, we will review (i) endogenous mechanisms of beta cell regeneration during steady state, stress and disease; (ii) efforts to stimulate endogenous regeneration and transdifferentiation; and (iii) exogenous methods of beta cell generation and transplantation.

Synthesis and in vivo behaviour of an exendin-4-based MRI probe capable of β-cell-dependent contrast enhancement in the pancreas

Global rates of diabetes mellitus are increasing, and treatment of the disease consumes a growing proportion of healthcare spending across the world. Pancreatic β-cells, responsible for insulin production, decline in mass in type 1 and, to a more limited degree, in type 2 diabetes. However, the extent and rate of loss in both diseases differs between patients resulting in the need for the development of novel diagnostic tools, which could quantitatively assess changes in mass of β-cells over time and potentially lead to earlier diagnosis and improved treatments. Exendin-4, a potent analogue of glucagon-like-peptide 1 (GLP-1), binds to the receptor GLP-1R, whose expression is enriched in β-cells. GLP-1R has thus been used in the past as a means of targeting probes for a wide variety of imaging modalities to the endocrine pancreas. However, exendin-4 conjugates designed specifically for MRI contrast agents are an under-explored area. In the present work, the synthesis and characterization of an exendin-4-dota(ga)-Gd(iii) complex, GdEx, is reported, along with its in vivo behaviour in healthy and in β-cell-depleted C57BL/6J mice. Compared to the ubiquitous probe, [Gd(dota)]-, GdEx shows selective uptake by the pancreas with a marked decrease in accumulation observed after the loss of β-cells elicited by deleting the microRNA processing enzyme, DICER. These results open up pathways towards the development of other targeted MRI contrast agents based on similar chemistry methodology.

Long Non-Coding RNAs as Key Modulators of Pancreatic β-Cell Mass and Function

Numerous studies have sought to decipher the genetic and other mechanisms contributing to β-cell loss and dysfunction in diabetes mellitus. However, we have yet to fully understand the etiology of the disease or to develop satisfactory treatments. Since the majority of diabetes susceptibility loci are mapped to non-coding regions within the genome, understanding the functions of non-coding RNAs in β-cell biology might provide crucial insights into the pathogenesis of type 1 (T1D) and type 2 (T2D) diabetes. During the past decade, numerous studies have indicated that long non-coding RNAs play important roles in the maintenance of β-cell mass and function. Indeed, lncRNAs have been shown to be involved in controlling β-cell proliferation during development and/or β-cell compensation in response to hyperglycaemia. LncRNAs such as TUG-1 and MEG3 play a role in both β-cell apoptosis and function, while others sensitize β-cells to apoptosis in response to stress signals. In addition, several long non-coding RNAs have been shown to regulate the expression of β-cell-enriched transcription factors in cis or in trans. In this review, we provide an overview of the roles of lncRNAs in maintaining β-function and mass, and discuss their relevance in the development of diabetes.

Transplantation of Islets of Langerhans into the Anterior Chamber of the Eye for Longitudinal In Vivo Imaging

Noninvasive in vivo imaging techniques are attractive tools to longitudinally study various aspects of islet of Langerhans physiology and pathophysiology. Unfortunately, most imaging modalities currently applicable for clinical use do not allow the comprehensive investigation of islet cell biology due to limitations in resolution and/or sensitivity, while high-resolution imaging technologies like laser scanning microscopy (LSM) lack the penetration depth to assess islets of Langerhans within the pancreas. Significant progress in this area was made by the combination of LSM with the anterior chamber of the mouse eye platform, utilizing the cornea as a natural body window to study cell physiology of transplanted islets of Langerhans. We here describe the transplantation and longitudinal in vivo imaging of islets of Langerhans in the anterior chamber of the mouse eye as a versatile tool to study different features of islet physiology in health and disease.

Islet Transplantation Imaging in vivo

Although islet transplantation plays an effective and powerful role in the treatment of diabetes, a large amount of islet grafts are lost at an early stage due to instant blood-mediated inflammatory reactions, immune rejection, and β-cell toxicity resulting from immunosuppressive agents. Timely intervention based on the viability and function of the transplanted islets at an early stage is crucial. Various islet transplantation imaging techniques are available for monitoring the conditions of post-transplanted islets. Due to the development of various imaging modalities and the continuous study of contrast agents, non-invasive islet transplantation imaging in vivo has made great progress. The tracing and functional evaluation of transplanted islets in vivo have thus become possible. However, most studies on contrast agent and imaging modalities are limited to animal experiments, and long-term toxicity and stability need further evaluation. Accordingly, the clinical application of the current achievements still requires a large amount of effort. In this review, we discuss the contrast agents for MRI, SPECT/PET, BLI/FI, US, MPI, PAI, and multimodal imaging. We further summarize the advantages and limitations of various molecular imaging methods.

The Innovative Medicines Initiative -10 Years of Public-Private Collaboration

The Innovative Medicines Initiative (IMI) is a public-private partnership between the European Union and the European pharmaceutical industry. Born of the necessity to foster collaboration between different stakeholders in order to address growing challenges in bringing new medicines to market and the rapidly evolving healthcare landscape, IMI has successfully delivered the radical collaboration needed to address these challenges. In this article we reflect on some of the major achievements of the programme by highlighting a few of the key projects funded and the progress they have made, as well as some of the lessons learnt in delivering such an ambitious partnership. Those that drove the foundation of IMI recognized that to address these challenges required not just ambitious scientific approaches, but also an awareness of societal needs. Therefore, actors from beyond the traditional pharmaceutical research communities would be needed. One of the key successes of IMI has been to foster radical collaboration between diverse public and private partners of all types, including large pharmaceutical companies, SMEs, regulators, patient organizations and public research institutions. It has achieved this by being a neutral platform where all partners are bound by the same rights and responsibilities. Since it began there has been an evolution in the understanding of what is considered “pre-competitive,” resulting in IMI projects now addressing all of the steps within the pharmaceutical development value chain. With this expansion in the types of projects supported by IMI, different actors from beyond the traditional pharmaceutical research family have been attracted to participate, enriching further the collaboration at the heart of the programme. Finally, such a complex programme brings with it challenges, and we reflect on some of the important learnings that should be applied to future collaborative models to ensure that they are as successful as possible and deliver the expected impact.

Imaging NF-κB activity in a murine model of early stage diabetes

Early pro-inflammatory signaling in the endocrine pancreas involves activation of NF-κB, which is believed to be important for determining the ultimate fate of β-cells and hence progression of type 1 diabetes (T1D). Thus, early non-invasive detection of NF-κB in pancreatic islets may serve as a potential strategy for monitoring early changes in pancreatic endocrine cells eventually leading to T1D. We investigated the feasibility of optical imaging of NF-κB transcription factor activation induced by low-dose streptozocin (LD-STZ) treatment in the immunocompetent SKH1 mouse model of early stage diabetes. In this model, we showed that the levels of NF-κB may be visualized and measured by fluorescence intensity of specific near-infrared (NIR) fluorophore-labeled oligodeoxyribonucleotide duplex (ODND) probes. In addition, NF-κB activation following LD-STZ treatment was validated using immunofluorescence and transgenic animals expressing NF-κB inducible imaging reporter. We showed that LD-STZ-treated SKH1 mice had significantly higher (2-3 times, P < .01) specific NIR FI in the nuclei and cytoplasm of islets cells than in non-treated control mice and this finding was corroborated by immunoblotting and electrophoretic mobility shift assays. Finally, using semi-quantitative confocal analysis of non-fixed pancreatic islet microscopy we demonstrated that ODND probes may be used to distinguish between the islets with high levels of NF-κB transcription factor and control islet cells.

Beta cells in type 1 diabetes: mass and function; sleeping or dead?

Histological analysis of donor pancreases coupled with measurement of serum C-peptide in clinical cohorts has challenged the idea that all beta cells are eventually destroyed in type 1 diabetes. These findings have raised a number of questions regarding how the remaining beta cells have escaped immune destruction, whether pools of 'sleeping' or dysfunctional beta cells could be rejuvenated and whether there is potential for new growth of beta cells. In this Review, we describe histological and in vivo evidence of persistent beta cells in type 1 diabetes and discuss the limitations of current methods to distinguish underlying beta cell mass in comparison with beta cell function. We highlight that evidence for new beta cell growth in humans many years from diagnosis is limited, and that this growth may be very minimal if at all present. We review recent contributions to the debate around beta cell abnormalities contributing to the pathogenesis of type 1 diabetes. We also discuss evidence for restoration of beta cell function, as opposed to mass, in recent-onset type 1 diabetes, but highlight the absence of data supporting functional recovery in the setting of long-duration diabetes. Finally, future areas of research are suggested to help resolve the source and phenotype of residual beta cells that persist in some, but not all, people with type 1 diabetes.

Ectonucleoside Triphosphate Diphosphohydrolase-3 Antibody Targets Adult Human Pancreatic β Cells for In Vitro and In Vivo Analysis

Identification of cell-surface markers specific to human pancreatic β cells would allow in vivo analysis and imaging. Here we introduce a biomarker, ectonucleoside triphosphate diphosphohydrolase-3 (NTPDase3), that is expressed on the cell surface of essentially all adult human β cells, including those from individuals with type 1 or type 2 diabetes. NTPDase3 is expressed dynamically during postnatal human pancreas development, appearing first in acinar cells at birth, but several months later its expression declines in acinar cells while concurrently emerging in islet β cells. Given its specificity and membrane localization, we utilized an NTPDase3 antibody for purification of live human β cells as confirmed by transcriptional profiling, and, in addition, for in vivo imaging of transplanted human β cells. Thus, NTPDase3 is a cell-surface biomarker of adult human β cells, and the antibody directed to this protein should be a useful new reagent for β cell sorting, in vivo imaging, and targeting.

Molecular imaging of β-cells: diabetes and beyond

Since diabetes is becoming a global epidemic, there is a great need to develop early β-cell specific diagnostic techniques for this disorder. There are two types of diabetes (i.e., type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM)). In T1DM, the destruction of pancreatic β-cells leads to reduced insulin production or even absolute insulin deficiency, which consequently results in hyperglycemia. Actually, a central issue in the pathophysiology of all types of diabetes is the relative reduction of β-cell mass (BCM) and/or impairment of the function of individual β-cells. In the past two decades, scientists have been trying to develop imaging techniques for noninvasive measurement of the viability and mass of pancreatic β-cells. Despite intense scientific efforts, only two tracers for positron emission tomography (PET) and one contrast agent for magnetic resonance (MR) imaging are currently under clinical evaluation. β-cell specific imaging probes may also allow us to precisely and specifically visualize transplanted β-cells and to improve transplantation outcomes, as transplantation of pancreatic islets has shown promise in treating T1DM. In addition, some of these probes can be applied to the preoperative detection of hidden insulinomas as well. In the present review, we primarily summarize potential tracers under development for imaging β-cells with a focus on tracers for PET, SPECT, MRI, and optical imaging. We will discuss the advantages and limitations of the various imaging probes and extend an outlook on future developments in the field.

Diet-induced β-cell insulin resistance results in reversible loss of functional β-cell mass

Although convincing in genetic models, the relevance of β-cell insulin resistance in diet-induced type 2 diabetes (T2DM) remains unclear. Exemplified by diabetes-prone, male, C57B1/6J mice being fed different combinations of Western-style diet, we show that β-cell insulin resistance occurs early during T2DM progression and is due to a combination of lipotoxicity and increased β-cell workload. Within 8 wk of being fed a high-fat, high-sucrose diet, mice became obese, developed impaired insulin and glucose tolerances, and displayed noncompensatory insulin release, due, at least in part, to reduced expression of syntaxin-1A. Through reporter islets transplanted to the anterior chamber of the eye, we demonstrated a concomitant loss of functional β-cell mass. When mice were changed from diabetogenic diet to normal chow diet, the diabetes phenotype was reversed, suggesting a remarkable plasticity of functional β-cell mass in the early phase of T2DM development. Our data reinforce the relevance of diet composition as an environmental factor determining different routes of diabetes progression in a given genetic background. Employing the in vivo reporter islet–monitoring approach will allow researchers to define key times in the dynamics of reversible loss of functional β-cell mass and, thus, to investigate the underlying, molecular mechanisms involved in the progression toward T2DM manifestation.—Paschen, M., Moede, T., Valladolid-Acebes, I., Leibiger, B., Moruzzi, N., Jacob, S., García-Prieto, C. F., Brismar, K., Leibiger, I. B., Berggren, P.-O. Diet-induced β-cell insulin resistance results in reversible loss of functional β-cell mass.

Pancreatic imaging using an antibody fragment targeting the zinc transporter type 8: a direct comparison with radio-iodinated Exendin-4

AIM

The zinc transporter 8 (ZnT8) has been suggested as a suitable target for non-invasive visualization of the functional pancreatic beta cell mass, due to both its pancreatic beta cell restricted expression and tight involvement in insulin secretion.

METHODS

In order to examine the potential of ZnT8 as a surrogate target for beta cell mass, we performed mRNA transcription analysis in pancreatic compartments. A novel ZnT8 targeting antibody fragment Ab31 was radiolabeled with iodine-125, and evaluated by in vitro autoradiography in insulinoma and pancreas as well as by in vivo biodistribution. The evaluation was performed in a direct comparison with radio-iodinated Exendin-4.

RESULTS

Transcription of the ZnT8 mRNA was higher in islets of Langerhans compared to exocrine tissue. Ab31 targeted ZnT8 in the cytosol and on the plasma membrane with 108 nM affinity. Ab31 was successfully radiolabeled with iodine-125 with high yield and > 95% purity. [¹²⁵I]Ab31 binding to insulinoma and pancreas was higher than for [¹²⁵I]Exendin-4, but could only by partially competed away by 200 nM Ab31 in excess. The in vivo uptake of [¹²⁵I]Ab31 was higher than [¹²⁵I]Exendin-4 in most tissues, mainly due to slower clearance from blood.

CONCLUSIONS

We report a first-in-class ZnT8 imaging ligand for pancreatic imaging. Development with respect to ligand miniaturization and radionuclide selection is required for further progress. Transcription analysis indicates ZnT8 as a suitable target for visualization of the human endocrine pancreas.

Kinetics of functional beta cell mass decay in a diphtheria toxin receptor mouse model of diabetes

Functional beta cell mass is an essential biomarker for the diagnosis and staging of diabetes. It has however proven technically challenging to study this parameter during diabetes progression. Here we have detailed the kinetics of the rapid decline in functional beta cell mass in the RIP-DTR mouse, a model of hyperglycemia resulting from diphtheria toxin induced beta cell ablation. A novel combination of imaging modalities was employed to study the pattern of beta cell destruction. Optical projection tomography of the pancreas and longitudinal in vivo confocal microscopy of islets transplanted into the anterior chamber of the eye allowed to investigate kinetics and tomographic location of beta cell mass decay in individual islets as well as at the entire islet population level. The correlation between beta cell mass and function was determined by complementary in vivo and ex vivo characterizations, demonstrating that beta cell function and glucose tolerance were impaired within the first two days following treatment when more than 50% of beta cell mass was remaining. Our results illustrate the importance of acquiring quantitative functional and morphological parameters to assess the functional status of the endocrine pancreas.

Intraocular in vivo imaging of pancreatic islet cell physiology/pathology

BACKGROUND

Diabetes mellitus has reached epidemic proportions and requires new strategies for treatment. Unfortunately, the efficacy of treatment regimens on maintaining/re-gaining functional beta cell mass can, at the present, only be determined indirectly. Direct monitoring of beta cell mass is complicated by the anatomy of the endocrine pancreas, which consists of thousands to a million of discrete micro-organs, i.e. islets of Langerhans, which are scattered throughout the pancreas.

SCOPE OF REVIEW

Here, we review the progress made over the last years using the anterior chamber of the eye as a transplantation site for functional imaging of pancreatic islet cells in the living organism. Islets engrafted on the iris are vascularized and innervated and the cornea, serving as a natural body-window, allows for microscopic, non-invasive, longitudinal evaluation of islet/beta cell function and survival with single-cell resolution in health and disease.

MAJOR CONCLUSIONS

Data provided by us and others demonstrate the high versatility of this imaging platform. The use of 'reporter islets' engrafted in the eye, reporting on the status of in situ endogenous islets in the pancreas of the same animal, allows the identification of key-events in the development and progression of diabetes. This will not only serve as a versatile research tool but will also lay the foundation for a personalized medicine approach and will serve as a screening platform for new drugs and/or treatment protocols. 'Metabolic' islet transplantation, in which islets engrafted in the eye replace the endogenous beta cells, will allow for the establishment of islet-specific transgenic models and 'humanized' mouse models as well as serving as the basis for a new clinical transplantation site for the cure of diabetes.

Spatial and quantitative datasets of the pancreatic β-cell mass distribution in lean and obese mice

A detailed understanding of pancreatic β-cell mass distribution is a key element to fully appreciate the pathophysiology of models of diabetes and metabolic stress. Commonly, such assessments have been performed by stereological approaches that rely on the extrapolation of two-dimensional data and provide very limited topological information. We present ex vivo optical tomographic data sets of the full β-cell mass distribution in cohorts of obese ob/ob mice and their lean controls, together with information about individual islet β-cell volumes, their three-dimensional coordinates and shape throughout the volume of the pancreas between 4 and 52 weeks of age. These data sets offer the currently most comprehensive public record of the β-cell mass distribution in the mouse. As such, they may serve as a quantitative and topological reference for the planning of a variety of in vivo or ex vivo experiments including computational modelling and statistical analyses. By shedding light on intra- and inter-lobular variations in β-cell mass distribution, they further provide a powerful tool for the planning of stereological sampling assessments.

Mass production of functional human pancreatic β-cells: why and how?

Diabetes (either type 1 or type 2) is due to insufficient functional β-cell mass. Research has, therefore, aimed to discover new ways to maintain or increase either β-cell mass or function. For this purpose, rodents have mainly been used as model systems and a large number of discoveries have been made. Meanwhile, although we have learned that rodent models represent powerful systems to model β-cell development, function and destruction, we realize that there are limitations when attempting to transfer the data to what is occurring in humans. Indeed, while human β-cells share many similarities with rodent β-cells, they also differ on a number of important parameters. In this context, developing ways to study human β-cell development, function and death represents an important challenge. This review will describe recent data on the development and use of convenient sources of human β-cells that should be useful tools to discover new ways to modulate functional β-cell mass in humans.

Pancreatic islet blood flow and its measurement

Pancreatic islets are richly vascularized, and islet blood vessels are uniquely adapted to maintain and support the internal milieu of the islets favoring normal endocrine function. Islet blood flow is normally very high compared with that to the exocrine pancreas and is autonomously regulated through complex interactions between the nervous system, metabolites from insulin secreting β-cells, endothelium-derived mediators, and hormones. The islet blood flow is normally coupled to the needs for insulin release and is usually disturbed during glucose intolerance and overt diabetes. The present review provides a brief background on islet vascular function and especially focuses on available techniques to measure islet blood perfusion. The gold standard for islet blood flow measurements in experimental animals is the microsphere technique, and its advantages and disadvantages will be discussed. In humans there are still no methods to measure islet blood flow selectively, but new developments in radiological techniques hold great hopes for the future.

Strategies for clinical trials in type 1 diabetes

During the past one to two decades, substantial progress has been made in our understanding of the immunopathology of type 1 diabetes (T1D) and the potential for immune interventions that can alter the natural history of the disease. This progress has resulted from the use of standardized study designs, endpoints, and, to a certain extent, mechanistic analyses in intervention trials in the setting of new-onset T1D. To date, most of these trials have involved single-agent interventions but, increasingly, future trials will test therapeutic combinations that are based on a compelling scientific rationale and testable mechanistic hypotheses. These increasingly complex trials will benefit from novel trial designs (such as factorial or adaptive designs), enhanced clinical endpoints that more directly assess islet pathology (such as β-cell death assays and islet or pancreatic imaging), improved responder analyses, and sophisticated mechanistic assays that provide deep phenotyping of lymphocyte subsets, gene expression profiling, in vitro T cell functional assessments, and antigen-specific responses. With this developing armamentarium of enhanced trial designs, endpoints, and clinical and mechanistic response analyses, we can expect substantial progress in better understanding the breakdown in immunologic tolerance in T1D and how to restore it to achieve significant and long-lasting preservation of islet function.