Distinctions between the islets of mice and men: implications for new therapies for type 1 and 2 diabetes

PDX1+ cell budding morphogenesis in a stem cell-derived islet spheroid system

Remarkable advances in protocol development have been achieved to manufacture insulin-secreting islets from human pluripotent stem cells (hPSCs). Distinct from current approaches, we devised a tunable strategy to generate islet spheroids enriched for major islet cell types by incorporating PDX1+ cell budding morphogenesis into staged differentiation. In this process that appears to mimic normal islet morphogenesis, the differentiating islet spheroids organize with endocrine cells that are intermingled or arranged in a core-mantle architecture, accompanied with functional heterogeneity. Through in vitro modelling of human pancreas development, we illustrate the importance of PDX1 and the requirement for EphB3/4 signaling in eliciting cell budding morphogenesis. Using this new approach, we model Mitchell-Riley syndrome with RFX6 knockout hPSCs illustrating unexpected morphogenesis defects in the differentiation towards islet cells. The tunable differentiation system and stem cell-derived islet models described in this work may facilitate addressing fundamental questions in islet biology and probing human pancreas diseases.

Advancing Diabetes Research: A Novel Islet Isolation Method from Living Donors

Pancreatic islet isolation is critical for type 2 diabetes research. Although -omics approaches have shed light on islet molecular profiles, inconsistencies persist; on the other hand, functional studies are essential, but they require reliable and standardized isolation methods. Here, we propose a simplified protocol applied to very small-sized samples collected from partially pancreatectomized living donors. Islet isolation was performed by digesting tissue specimens collected during surgery within a collagenase P solution, followed by a Lympholyte density gradient separation; finally, functional assays and staining with dithizone were carried out. Isolated pancreatic islets exhibited functional responses to glucose and arginine stimulation mirroring donors' metabolic profiles, with insulin secretion significantly decreasing in diabetic islets compared to non-diabetic islets; conversely, proinsulin secretion showed an increasing trend from non-diabetic to diabetic islets. This novel islet isolation method from living patients undergoing partial pancreatectomy offers a valuable opportunity for targeted study of islet physiology, with the primary advantage of being time-effective and successfully preserving islet viability and functionality. It enables the generation of islet preparations that closely reflect donors' clinical profiles, simplifying the isolation process and eliminating the need for a Ricordi chamber. Thus, this method holds promises for advancing our understanding of diabetes and for new personalized pharmacological approaches.

Bridging the Gap: Pancreas Tissue Slices From Organ and Tissue Donors for the Study of Diabetes Pathogenesis

Over the last two decades, increased availability of human pancreatic tissues has allowed for major expansions in our understanding of islet biology in health and disease. Indeed, studies of fixed and frozen pancreatic tissues, as well as efforts using viable isolated islets obtained from organ donors, have provided significant insights toward our understanding of diabetes. However, the procedures associated with islet isolation result in distressed cells that have been removed from any surrounding influence. The pancreas tissue slice technology was developed as an in situ approach to overcome certain limitations associated with studies on isolated islets or fixed tissue. In this Perspective, we discuss the value of this novel platform and review how pancreas tissue slices, within a short time, have been integrated in numerous studies of rodent and human islet research. We show that pancreas tissue slices allow for investigations in a less perturbed organ tissue environment, ranging from cellular processes, over peri-islet modulations, to tissue interactions. Finally, we discuss the considerations and limitations of this technology in its future applications. We believe the pancreas tissue slices will help bridge the gap between studies on isolated islets and cells to the systemic conditions by providing new insight into physiological and pathophysiological processes at the organ level.

ARTICLE HIGHLIGHTS

Human pancreas tissue slices represent a novel platform to study human islet biology in close to physiological conditions. Complementary to established technologies, such as isolated islets, single cells, and histological sections, pancreas tissue slices help bridge our understanding of islet physiology and pathophysiology from single cell to intact organ. Diverse sources of viable human pancreas tissue, each with distinct characteristics to be considered, are available to use in tissue slices for the study of diabetes pathogenesis.

Global proteomics reveals insulin abundance as a marker of human islet homeostasis alterations

AIM

The variation in quality between the human islet samples represents a major problem for research, especially when used as control material. The assays assessing the quality of human islets used in research are non-standardized and limited, with many important parameters not being consistently assessed. High-throughput studies aimed at characterizing the diversity and segregation markers among apparently functionally healthy islet preps are thus a requirement. Here, we designed a pilot study to comprehensively identify the diversity of global proteome signatures and the deviation from normal homeostasis in randomly selected human-isolated islet samples.

METHODS

By using Tandem Mass Tag 16-plex proteomics, we focused on the recurrently observed disparity in the detected insulin abundance between the samples, used it as a segregating parameter, and analyzed the correlated changes in the proteome signature and homeostasis by pathway analysis.

RESULTS

In this pilot study, we showed that insulin protein abundance is a predictor of human islet homeostasis and quality. This parameter is independent of other quality predictors within their acceptable range, thus being able to further stratify islets samples of apparent good quality. Human islets with low amounts of insulin displayed changes in their metabolic and signaling profile, especially in regard to energy homeostasis and cell identity maintenance. We further showed that xenotransplantation into diabetic hosts is not expected to improve the pre-transplantation signature, as it has a negative effect on energy balance, antioxidant activity, and islet cell identity.

CONCLUSIONS

Insulin protein abundance predicts significant changes in human islet homeostasis among random samples of apparently good quality.

Regeneration of Pancreatic Beta Cells by Modulation of Molecular Targets Using Plant-Derived Compounds: Pharmacological Mechanisms and Clinical Potential

Type 2 diabetes (T2D) is characterized by pancreatic beta-cell dysfunction, increased cell death and loss of beta-cell mass despite chronic treatment. Consequently, there has been growing interest in developing beta cell-centered therapies. Beta-cell regeneration is mediated by augmented beta-cell proliferation, transdifferentiation of other islet cell types to functional beta-like cells or the reprograming of beta-cell progenitors into fully differentiated beta cells. This mediation is orchestrated by beta-cell differentiation transcription factors and the regulation of the cell cycle machinery. This review investigates the beta-cell regenerative potential of antidiabetic plant extracts and phytochemicals. Various preclinical studies, including in vitro, in vivo and ex vivo studies, are highlighted. Further, the potential regenerative mechanisms and the intra and extracellular mediators that are of significance are discussed. Also, the potential of phytochemicals to translate into regenerative therapies for T2D patients is highlighted, and some suggestions regarding future perspectives are made.

Diversity and biological activities of medicinal plants of Santiago island (Cabo Verde)

Plants continue to constitute key elements of medical practice in West African countries. The Cabo Verde archipelago hosts a great diversity of medicinal plants and local markets are considered important sites for trading plants harvested by rural communities. This study has two main goals: (i) to assess the medicinal uses of native species in Santiago, the biggest island of the archipelago, and (ii) to evaluate the antioxidant, antimicrobial and antidiabetic/antihyperglycemic activities of two native trees (Tamarix senegalensis and Sideroxylon marginatum) used in traditional medicine and traded in local markets. Our results revealed that on Santiago Island, 24 native plants are used in traditional medicine. The main uses of these species (e.g., forage, timber, food and fibres), their medicinal applications, the plant parts used, their mode of administration and conservation status are presented here for the first time. Moreover, the pharmacological characterization of two native tree species revealed that hydroethanolic extracts were richer in phenolic compounds and more active than their aqueous counterparts. All the studied extracts revealed significant antioxidant properties (DPPH and FRAP assays) and were generally moderately active against Gram-positive bacteria. All the extracts inhibited the activities of the carbohydrate digestive enzymes α-glucosidase and α-amylase in a dose-dependent manner. For α-glucosidase, the detected inhibitory activity (IC₅₀ values from 2.0 ± 0.2 μg/mL to 9.9 ± 1.2 μg/mL) was significantly higher than that of acarbose, suggesting that extracts of both species can delay glucose absorption, thereby assisting in slowing down the progression of diabetes. Our findings highlight the crucial importance that medicinal plants have for the Cabo Verdean population, while also raising awareness on the need for sustainable use and conservation of native flora, and of tree species traded in local markets in particular.

Hemorheological and Microcirculatory Relations of Acute Pancreatitis

Acute pancreatitis still means a serious challenge in clinical practice. Its pathomechanism is complex and has yet to be fully elucidated. Rheological properties of blood play an important role in tissue perfusion and show non-specific changes in acute pancreatitis. An increase in blood and plasma viscosity, impairment of red blood cell deformability, and enhanced red blood cell aggregation caused by metabolic, inflammatory, free radical-related changes and mechanical stress contribute to the deterioration of the blood flow in the large vessels and also in the microcirculation. Revealing the significance of these changes in acute pancreatitis may better explain the pathogenesis and optimize the therapy. In this review, we give an overview of the role of impaired microcirculation by changes in hemorheological properties in acute pancreatitis.

Glucagon receptor antagonist volagidemab in type 1 diabetes: a 12-week, randomized, double-blind, phase 2 trial

Hyperglucagonemia contributes to hyperglycemia in patients with type 1 diabetes (T1D); however, novel therapeutics that block glucagon action could improve glycemic control. This phase 2 study evaluated the safety and efficacy of volagidemab, an antagonistic monoclonal glucagon receptor (GCGR) antibody, as an adjunct to insulin therapy in adults with T1D. The primary endpoint was change in daily insulin use at week 12. Secondary endpoints included changes in hemoglobin A1c (HbA1c) at week 13, in average daily blood glucose concentration and time within target range as assessed by continuous blood glucose monitoring (CGM) and seven-point glucose profile at week 12, incidence of hypoglycemic events, the proportion of subjects who achieve HbA1c reduction of ≥0.4%, volagidemab drug concentrations and incidence of anti-drug antibodies. Eligible participants (n = 79) were randomized to receive weekly subcutaneous injections of placebo, 35 mg volagidemab or 70 mg volagidemab. Volagidemab produced a reduction in total daily insulin use at week 12 (35 mg volagidemab: -7.59 units (U) (95% confidence interval (CI) -11.79, -3.39; P = 0.040 versus placebo); 70 mg volagidemab: -6.64 U (95% CI -10.99, -2.29; P = 0.084 versus placebo); placebo: -1.27 U (95% CI -5.4, 2.9)) without meeting the prespecified significance level (P < 0.025). At week 13, the placebo-corrected reduction in HbA1c percentage was -0.53 (95% CI -0.89 to -0.17, nominal P = 0.004) in the 35 mg volagidemab group and -0.49 (95% CI -0.85 to -0.12, nominal P = 0.010) in the 70 mg volagidemab group. No increase in hypoglycemia was observed with volagidemab therapy; however, increases in serum transaminases, low-density lipoprotein (LDL)-cholesterol and blood pressure were observed. Although the primary endpoint did not meet the prespecified significance level, we believe that the observed reduction in HbA1c and tolerable safety profile provide a rationale for further randomized studies to define the long-term efficacy and safety of volagidemab in patients with T1D.

Endoplasmic Reticulum Stress and Dysregulated Autophagy in Human Pancreatic Beta Cells

Pancreatic beta cell homeostasis is crucial for the synthesis and secretion of insulin; disruption of homeostasis causes diabetes, and is a treatment target. Adaptation to endoplasmic reticulum (ER) stress through the unfolded protein response (UPR) and adequate regulation of autophagy, which are closely linked, play essential roles in this homeostasis. In diabetes, the UPR and autophagy are dysregulated, which leads to beta cell failure and death. Various studies have explored methods to preserve pancreatic beta cell function and mass by relieving ER stress and regulating autophagic activity. To promote clinical translation of these research results to potential therapeutics for diabetes, we summarize the current knowledge on ER stress and autophagy in human insulin-secreting cells.

Feline Adipose Derived Multipotent Stromal Cell Transdifferentiation Into Functional Insulin Producing Cell Clusters

Diabetes mellitus (DM) is one of the most prevalent feline endocrinopathies, affecting up to 1% of pet cats. De novo generation of functional insulin producing cell (IPC) clusters via transdifferentiation of feline adipose-derived multipotent stromal cells (ASCs) may not only provide a viable, functional cell therapy for feline DM, but may also serve as a platform for developing a comparable human treatment given feline and human DM similarities. Cells were induced to form IPCs with a novel, three-stage culture process with stromal or differentiation medium under static and dynamic conditions. Clusters were evaluated for intracellular zinc, viability, intracellular insulin, glucagon, and somatostatin, ultrastructure, glucose stimulated insulin secretion in the presence or absence of theophylline, and protein and gene expression. Isolated cells were multipotent, and cell clusters cultured in both media had robust cell viability. Those cultured in differentiation medium contained zinc and mono- or polyhormonal α-, β-, and δ-like cells based on immunohistochemical labeling and Mallory-Heidenhan Azan-Gomori’s staining. Ultrastructurally, cell clusters cultured in differentiation medium contained insulin granules within vesicles, and clusters had a concentration-dependent insulin response to glucose in the presence and absence of theophylline which increased both insulin secretion and intracellular content. Expression of NK6.1, Pax6, Isl1, Glut2, RAB3A, glucagon, insulin, and somatostatin increased with differentiation stage for both sexes, and expression of nestin at stages 1 and 2 and Neurod1 at stage 2 was higher in cells from female donors. The cluster insulin secretion responses and endocrine and oncogene gene expression profiles were inconsistent with insulinoma characteristics. A total of 180 proteins were upregulated in differentiated clusters, and the majority were associated with biological regulation, metabolic processes, or stimulus response. Dynamic culture of IPC clusters resulted in clusters composed of cells primarily expressing insulin that released higher insulin with glucose stimulation than those in static culture. Collectively, the results of this study support generation of functional IPC clusters using feline ASCs isolated from tissues removed during routine sterilization. Further, cluster functionality is enhanced with dynamic, motion-driven shear stress. This work establishes a foundation for development of strategies for IPC therapy for short or long-term diabetes treatment and may represent an option to study prevention and treatment of diabetes across species.

G protein-coupled receptors as regulators of pancreatic islet functionality

Glucose homeostasis is maintained by hormones secreted from different types of pancreatic islets and its dysregulation can result in diseases including diabetes mellitus. The secretion of hormones from pancreatic islets is highly complex and tightly controlled by G protein-coupled receptors (GPCRs). Moreover, GPCR signaling may play a role in enhancing islet cell replication and proliferation. Thus, targeting GPCRs offers a promising strategy for regulating the functionality of pancreatic islets. Here, available RNAseq datasets from human and mouse islets were used to identify the GPCR expression profile and the impact of GPCR signaling for normal islet functionality is discussed.

Pancreatic β cell regeneration induced by clinical and preclinical agents

Diabetes, one of the most common chronic diseases in the modern world, has pancreatic β cell deficiency as a major part of its pathophysiological mechanism. Pancreatic regeneration is a potential therapeutic strategy for the recovery of β cell loss. However, endocrine islets have limited regenerative capacity, especially in adult humans. Almost all hypoglycemic drugs can protect β cells by inhibiting β cell apoptosis and dedifferentiation via correction of hyperglycemia and amelioration of the consequent inflammation and oxidative stress. Several agents, including glucagon-like peptide-1 and γ-aminobutyric acid, have been shown to promote β cell proliferation, which is considered the main source of the regenerated β cells in adult rodents, but with less clarity in humans. Pancreatic progenitor cells might exist and be activated under particular circumstances. Artemisinins and γ-aminobutyric acid can induce α-to-β cell conversion, although some disputes exist. Intestinal endocrine progenitors can transdeterminate into insulin-producing cells in the gut after FoxO1 deletion, and pharmacological research into FoxO1 inhibition is ongoing. Other cells, including pancreatic acinar cells, can transdifferentiate into β cells, and clinical and preclinical strategies are currently underway. In this review, we summarize the clinical and preclinical agents used in different approaches for β cell regeneration and make some suggestions regarding future perspectives for clinical application.

Pancreatic Progenitors: There and Back Again

Adult pancreatic regeneration is one of the most contentious topics in modern biology. The long-held view that the islets of Langerhans can be replenished throughout adult life through the reactivation of ductal progenitor cells has been replaced over the past decade by the now prevailing notion that regeneration does not involve progenitors and occurs only through the duplication of pre-existing mature cells. Here we dissect the limitations of lineage tracing (LT) to draw categorical conclusions about pancreatic regeneration, especially in view of emerging evidence that traditional lineages are less homogeneous and cell fates more dynamic than previously thought. This new evidence further suggests that the two competing hypotheses about regeneration are not mutually exclusive.

The triggering pathway to insulin secretion: Functional similarities and differences between the human and the mouse β cells and their translational relevance

In β cells, stimulation by metabolic, hormonal, neuronal, and pharmacological factors is coupled to secretion of insulin through different intracellular signaling pathways. Our knowledge about the molecular machinery supporting these pathways and the patterns of signals it generates comes mostly from rodent models, especially the laboratory mouse. The increased availability of human islets for research during the last few decades has yielded new insights into the specifics in signaling pathways leading to insulin secretion in humans. In this review, we follow the most central triggering pathway to insulin secretion from its very beginning when glucose enters the β cell to the calcium oscillations it produces to trigger fusion of insulin containing granules with the plasma membrane. Along the way, we describe the crucial building blocks that contribute to the flow of information and focus on their functional role in mice and humans and on their translational implications.

The species origin of the cellular microenvironment influences markers of beta cell fate and function in EndoC-βH1 cells

Interaction between islet cell subtypes and the extracellular matrix influences beta-cell function in mammals. The tissue architecture of rodent islets is very different to that of human islets; cell-to-cell communication and interaction with the extracellular matrix may vary between species. In this work, we have compared the responses of the human EndoC-βH1 cell line to non-human and human-derived growth matrices in terms of growth morphology, gene expression and glucose-stimulated insulin secretion (GSIS). EndoC-βH1 cells demonstrated a greater tendency to form cell clusters when cultured in a human microenvironment and exhibited reduced alpha cell markers at the mRNA level; mean expression difference - 0.23 and - 0.51; p = 0.009 and 0.002 for the Aristaless-related homeobox (ARX) and Glucagon (GCG) genes respectively. No differences were noted in the protein expression of mature beta cell markers such as Pdx1 and NeuroD1 were noted in EndoC-βH1 cells grown in a human microenvironment but cells were however more sensitive to glucose (4.3-fold increase in insulin secretion following glucose challenge compared with a 1.9-fold increase in cells grown in a non-human microenvironment; p = 0.0003). Our data suggests that the tissue origin of the cellular microenvironment has effects on the function of EndoC-βH1 cells in vitro, and the use of a more human-like culture microenvironment may bring benefits in terms of increased physiological relevance.

All mixed up: defining roles for β-cell subtypes in mature islets

Following differentiation during fetal development, β cells further adapt to their postnatal role through functional maturation. While adult islets are thought to contain functionally mature β cells, recent analyses of transgenic rodent and human pancreata reveal a number of novel heterogeneity markers in mammalian β cells. The marked heterogeneity long after maturation raises the prospect that diverse populations harbor distinct roles aside from glucose-stimulated insulin secretion. In this review, we outline our current understanding of the β-cell maturation process, emphasize recent literature on novel heterogeneity markers, and offer perspectives on reconciling the findings from these two areas.

A rhamnan-type sulfated polysaccharide with novel structure from Monostroma angicava Kjellm (Chlorophyta) and its bioactivity

A homogeneous polysaccharide was obtained from Monostroma angicava Kjellm by water extraction, preparative anion-exchange and size-exclusion chromatography. Results of chemical and spectroscopic analyses showed that the polysaccharide was a glucuronic acid-containing rhamnan-type sulfated polysaccharide. The backbone mainly consisted of →3)-α-l-Rhap-(1→ and →2)-α-l-Rhap-(1→ residues, partially sulfated at C-2 of →3)-α-l-Rhap-(1→ and C-3/C-4 of →2)-α-l-Rhap-(1→. The branching contained unsulfated or monosulfated 3-linked, 2-linked, 4-linked α-l-rhamnose and terminal β-d-glucuronic acid residues. The polysaccharide had strong antidiabetic activity assessed by glucose consumption, total cholesterol and triglyceride levels using human hepatocellular carcinoma (HepG2) and insulin-resistant HepG2 cells. The polysaccharide exhibited high anticoagulant property by activated partial thromboplastin time and thrombin time assays, and possessed high fibrin(ogen)olytic activity evaluated by plasminogen activator inhibitior-1, fibrin(ogen) degradation products and D-dimer levels using rats plasma. The investigation demonstrated that the polysaccharide from Monostroma angicava Kjellm was a novel sulfated rhamnan and could be a potential antidiabetic and anticoagulant polysaccharide.

Histological changes in endocrine and exocrine pancreatic tissue from patients exposed to incretin-based therapies

AIMS

Incretin-based therapies have been associated with an increased risk of pancreatitis. Recently, various histological abnormalities have been reported in human pancreatic tissue from brain-dead organ donors who had been exposed to incretin-based drugs. In the present study we examined pancreatic tissue collected at surgery.

METHODS

Human pancreatic tissue from 7 type 2-diabetic patients treated with incretin-based drugs (type 2-I), 6 diabetic patients without incretin treatment (type 2-NI), 11 patients without diabetes (no diabetes group) and 9 brain-dead organ donors (BDOD group) was examined.

RESULTS

Fractional beta-cell area was reduced in the type 2-NI group compared to the group without diabetes (P < .05), but there was no difference compared to the type 2-I patients. Alpha-cell area (P = .30), beta-cell replication (P = .17) and alpha-cell replication (P = .91) were not different. There were also no differences in acinar cell (P = .13) and duct cell replication (P = .099). Insulin-positive duct cells were more frequent in the type 2-I and the BDOD groups (P = .034). No co-expression of insulin and glucagon was detected. Pancreatic intraepithelial neoplasia (PanIN) lesions were very rare, all low-grade (PanIN 1a and 1b) and tended to occur more frequently in the type 2-I group (P = .084).

CONCLUSIONS

The present results did not reveal marked histological abnormalities in the pancreas of incretin-treated patients with type 2 diabetes. Low numbers of specimens available and a large inter-individual variability of the findings warrant caution regarding the interpretation of histological data concerning drug effects on the human pancreas.

A Single-Cell Transcriptomic Map of the Human and Mouse Pancreas Reveals Inter- and Intra-cell Population Structure

Although the function of the mammalian pancreas hinges on complex interactions of distinct cell types, gene expression profiles have primarily been described with bulk mixtures. Here we implemented a droplet-based, single-cell RNA-seq method to determine the transcriptomes of over 12,000 individual pancreatic cells from four human donors and two mouse strains. Cells could be divided into 15 clusters that matched previously characterized cell types: all endocrine cell types, including rare epsilon-cells; exocrine cell types; vascular cells; Schwann cells; quiescent and activated stellate cells; and four types of immune cells. We detected subpopulations of ductal cells with distinct expression profiles and validated their existence with immuno-histochemistry stains. Moreover, among human beta- cells, we detected heterogeneity in the regulation of genes relating to functional maturation and levels of ER stress. Finally, we deconvolved bulk gene expression samples using the single-cell data to detect disease-associated differential expression. Our dataset provides a resource for the discovery of novel cell type-specific transcription factors, signaling receptors, and medically relevant genes.

Interleukin-6 as a potential positive modulator of human beta-cell function: an exploratory analysis-the Verona Newly Diagnosed Type 2 Diabetes Study (VNDS) 6

AIMS

Recent studies in mouse models of T2D showed that interleukin-6 (IL-6), released from skeletal muscle, is associated with increased glucose-dependent insulin secretion. Few data currently exist exploring the relationship between IL-6 and beta-cell function in humans. We investigated whether IL-6 is positively associated with beta-cell function in newly diagnosed T2D. We extended the same analyses to IL-10, because it regulated similarly to IL-6 in skeletal muscle, and TNF-α and C-reactive protein (CRP), as general biomarkers of inflammation.

METHODS

In 330 VNDS participants, we assessed (1) basal plasma concentrations of IL-6, IL-10, TNF-α, and CRP; (2) beta-cell function, estimated by OGTT minimal modeling and expressed as derivative (DC) and proportional control (PC); (3) insulin sensitivity, by euglycemic insulin clamp.

RESULTS

IL-6 was positively associated with PC in both univariate analysis (p = 0.04) and after adjustment for age, sex, BMI, HbA1c, and M-clamp (p = 0.01). HbA1c was the major independent contributor to the overall variance of PC (16 %), followed by BMI and IL-6 (~2 % each). Similar results were obtained for IL-10 (p = 0.048, univariate; p = 0.04, fully adjusted). TNF-α and CRP were not significantly associated with any component of beta-cell function.

CONCLUSIONS

Our data are the first evidence in human subjects that an endocrine loop involving IL-6 may act as positive modulator of glucose-dependent insulin secretion. Further functional studies are needed to corroborate IL-6 system as a potential druggable target in diabetes.

CLINICAL TRIAL REGISTRATION NUMBER

NCT01526720 ( http://www.clinicaltrial.gov ).

Evaluation of immunohistochemical staining for glucagon in human pancreatic tissue

Immunohistochemistry (IHC) and immunofluorescence (IF) staining techniques are important diagnostic tools of anatomic pathology in the clinical setting and widely used analytical tools in research laboratories. In diabetes research, they are routinely used for the assessment of beta- and alpha-cell mass, for assessment of endocrine cell distribution within the pancreas, for evaluation of islet composition and islet morphology. Here, we present the evaluation of IHC techniques for the detection of alpha-cells in human pancreatic tissue. We compared the Horse Radish Peroxidase (HRP)-based method utilizing DAB Peroxidase Substrate to the Alkaline Phosphatase (AP)-based method utilizing Vector Red substrate. We conclude that HRP-DAB staining is a robust and reliable method for detection of alpha-cells using either rabbit polyclonal or mouse monoclonal anti-glucagon antibodies. However, AP-Vector Red staining should be used with caution, because it is affected by the dehydration with ethanol and toluene preceding the mounting of slides with Permount mounting medium. When AP-Vector Red is a preferable method for alpha-cell labeling, slides should be mounted using aqueous mounting medium or, alternatively, they could be air-dried before permanent mounting.

In vitro and in vivo hypoglycemic effects of brown algal fucoidans

The inhibition of α-glucosidase is an effective therapeutic approach for type 2 diabetes mellitus that involves decreasing postprandial hyperglycemia. In the present study, the α-glucosidase and α-amylase inhibitory effects of 11 fucoidans extracted from different brown seaweeds were evaluated. Although no significant α-amylase inhibition was observed, fucoidan from Fucus vesiculosus (FvF) showed the highest α-glucosidase inhibitory activity, with an IC50 value of 67.9 μg/mL. In addition, FvF at a concentration of 200 μg/mL displayed very mild cytotoxicity to IEC-6 cells as indicated by the MTT assay. An in vivo study indicated that FvF decreased the fasting blood glucose and hemoglobin A1c (HbA1c) levels of db/db mice, with minimal effect on their weight. Therefore, our present in vitro and in vivo studies demonstrated that FvF could be a promising α-glucosidase inhibitor for the treatment of type 2 diabetes mellitus.

Membrane Potential and Calcium Dynamics in Beta Cells from Mouse Pancreas Tissue Slices: Theory, Experimentation, and Analysis

Beta cells in the pancreatic islets of Langerhans are precise biological sensors for glucose and play a central role in balancing the organism between catabolic and anabolic needs. A hallmark of the beta cell response to glucose are oscillatory changes of membrane potential that are tightly coupled with oscillatory changes in intracellular calcium concentration which, in turn, elicit oscillations of insulin secretion. Both membrane potential and calcium changes spread from one beta cell to the other in a wave-like manner. In order to assess the properties of the abovementioned responses to physiological and pathological stimuli, the main challenge remains how to effectively measure membrane potential and calcium changes at the same time with high spatial and temporal resolution, and also in as many cells as possible. To date, the most wide-spread approach has employed the electrophysiological patch-clamp method to monitor membrane potential changes. Inherently, this technique has many advantages, such as a direct contact with the cell and a high temporal resolution. However, it allows one to assess information from a single cell only. In some instances, this technique has been used in conjunction with CCD camera-based imaging, offering the opportunity to simultaneously monitor membrane potential and calcium changes, but not in the same cells and not with a reliable cellular or subcellular spatial resolution. Recently, a novel family of highly-sensitive membrane potential reporter dyes in combination with high temporal and spatial confocal calcium imaging allows for simultaneously detecting membrane potential and calcium changes in many cells at a time. Since the signals yielded from both types of reporter dyes are inherently noisy, we have developed complex methods of data denoising that permit for visualization and pixel-wise analysis of signals. Combining the experimental approach of high-resolution imaging with the advanced analysis of noisy data enables novel physiological insights and reassessment of current concepts in unprecedented detail.

The anti-diabetic effects of GLP-1-gastrin dual agonist ZP3022 in ZDF rats

AIMS/HYPOTHESIS

Combination treatment with exendin-4 and gastrin has proven beneficial in treatment of diabetes and preservation of beta cell mass in diabetic mice. Here, we examined the chronic effects of a GLP-1-gastrin dual agonist ZP3022 on glycemic control and beta cell dysfunction in overtly diabetic Zucker Diabetic Fatty (ZDF) rats.

METHODS

ZDF rats aged 11 weeks were dosed s.c., b.i.d. for 8 weeks with vehicle, ZP3022, liraglutide, exendin-4, or gastrin-17 with or without exendin-4. Glycemic control was assessed by measurements of HbA1c and blood glucose levels, as well as glucose tolerance during an oral glucose tolerance test (OGTT). Beta cell dynamics were examined by morphometric analyses of beta and alpha cell fractions.

RESULTS

ZP3022 improved glycemic control as measured by terminal HbA1c levels (6.2±0.12 (high dose) vs. 7.9±0.07% (vehicle), P<0.001), as did all treatments, except gastrin-17 monotherapy. In contrast, only ZP3022, exendin-4 and combination treatment with exendin-4 and gastrin-17 significantly improved glucose tolerance and increased insulin levels during an OGTT. Moreover, only ZP3022 significantly enhanced the beta cell fraction in ZDF rats, a difference of 41%, when compared to the vehicle group (0.31±0.03 vs. 0.22±0.02%, respectively, P<0.05).

CONCLUSION

These data suggest that ZP3022 may have therapeutic potential in the prevention/delay of beta cell dysfunction in type 2 diabetes.

Engineering of microscale three-dimensional pancreatic islet models in vitro and their biomedical applications

Diabetes now is the most common chronic disease in the world inducing heavy burden for the people's health. Based on this, diabetes research such as islet function has become a hot topic in medical institutes of the world. Today, in medical institutes, the conventional experiment platform in vitro is monolayer cell culture. However, with the development of micro- and nano-technologies, several microengineering methods have been developed to fabricate three-dimensional (3D) islet models in vitro which can better mimic the islet of pancreases in vivo. These in vitro islet models have shown better cell function than monolayer cells, indicating their great potential as better experimental platforms to elucidate islet behaviors under both physiological and pathological conditions, such as the molecular mechanisms of diabetes and clinical islet transplantation. In this review, we present the state-of-the-art advances in the microengineering methods for fabricating microscale islet models in vitro. We hope this will help researchers to better understand the progress in the engineering 3D islet models and their biomedical applications such as drug screening and islet transplantation.

Human adipose-derived stromal/stem cells protect against STZ-induced hyperglycemia: analysis of hASC-derived paracrine effectors

Adipose-derived stromal/stem cells (ASCs) ameliorate hyperglycemia in rodent models of islet transplantation and autoimmune diabetes, yet the precise human ASC (hASC)-derived factors responsible for these effects remain largely unexplored. Here, we show that systemic administration of hASCs improved glucose tolerance, preserved β cell mass, and increased β cell proliferation in streptozotocin-treated nonobese diabetic/severe combined immunodeficient mice. Coculture experiments combining mouse or human islets with hASCs demonstrated that islet viability and function were improved by hASCs following prolonged culture or treatment with proinflammatory cytokines. Analysis of hASC-derived factors revealed vascular endothelial growth factor and tissue inhibitor of metalloproteinase 1 (TIMP-1) to be highly abundant factors secreted by hASCs. Notably, TIMP-1 secretion increased in the presence of islet stress from cytokine treatment, while TIMP-1 blockade was able to abrogate in vitro prosurvival effects of hASCs. Following systemic administration by tail vein injection, hASCs were detected in the pancreas and human TIMP-1 was increased in the serum of injected mice, while recombinant TIMP-1 increased viability in INS-1 cells treated with interleukin-1beta, interferon-gamma, and tumor necrosis factor alpha. In aggregate, our data support a model whereby factors secreted by hASCs, such as TIMP-1, are able to mitigate against β cell death in rodent and in vitro models of type 1 diabetes through a combination of local paracrine as well as systemic effects.

Structural similarities and differences between the human and the mouse pancreas

Mice remain the most studied animal model in pancreas research. Since the findings of this research are typically extrapolated to humans, it is important to understand both similarities and differences between the 2 species. Beside the apparent difference in size and macroscopic organization of the organ in the 2 species, there are a number of less evident and only recently described differences in organization of the acinar and ductal exocrine tissue, as well as in the distribution, composition, and architecture of the endocrine islets of Langerhans. Furthermore, the differences in arterial, venous, and lymphatic vessels, as well as innervation are potentially important. In this article, the structure of the human and the mouse pancreas, together with the similarities and differences between them are reviewed in detail in the light of conceivable repercussions for basic research and clinical application.

A Simple Method to Replace Islet Equivalents for Volume Quantification of Human Islets

Human islets come in a variety of sizes and shapes, and the total volume of islets used for research or clinical transplants must be estimated in a manner that is simple and valid. Islet equivalent (IEQ) measurements are the standard estimate of islet volume. We published a new method (the Kansas method) for estimating rat islet volume using cell numbers that was reliable and valid. Here we modified the method for human islets. We measured the dimensions of isolated human islets showing that they are not spherical and became less so in larger islets, with an average smallest/largest diameter ratio of 0.73 in large islets and 0.85 in small islets. Human islets were individually loaded into 96-well plates, dissociated into single cells, and the total cell number per islet determined with computer-assisted cytometry. Based on the counted cell number per islet, a regression model was created to convert islet diameter to cell number with a high R(2) value (0.99). Separate regression equations for male and female donors or young and old donors were not significantly different than the pooled data and did not improve the regression values. There was an inverse correlation between the cell number per IEQ and islet size. The Kansas method was validated with ATP/cell and cell viability data. Compared to the actual cell count, conventional IEQ measurements overestimated tissue volume of large islets by nearly double. Examples of differences in results obtained from the same data sets normalized to IEQ or the Kansas method included viability and insulin secretion concentrations. The implications of the error associated with the current IEQ method of volume estimation are discussed.

Proposal for generating new beta cells in a muted immune environment for type 1 diabetes

BACKGROUND

Over the past decade, many immune tolerance agents have shown promise in the non-obese diabetic mouse model for prevention and reversal of type 1 diabetes but have not been successful in clinical trials among recently diagnosed type 1 patients. The trials from decades ago using Cyclosporine A in significantly lower dosages than used for organ transplantation and in similar dosages that have increased T regulatory cell populations in conditions such as atopic dermatitis, demonstrated very high initial insulin-free remission rates when administered immediately after diagnosis. Over time, all newly diagnosed type 1 patients given Cyclosporine A required insulin. Human trials with immune tolerance agents suggest that in addition to an immune tolerance agent, a beta cell regeneration agent may also be necessary to induce long-lasting remission among patients with recent onset type 1 diabetes.

METHODS

A randomized, double-blind prospective trial among recent onset type 1 diabetes patients has been designed using Cyclosporine A and a proton-pump inhibitor, which increases gastrin levels and has been shown to work through the Reg receptor to transform pancreatic duct cells into islets.

Mouse Models of β-cell KATP Channel Dysfunction

ATP-sensitive K⁺ (K_ATP) channels in pancreatic β-cells couple glucose metabolism to insulin secretion. Reduced K_ATP channel activity produces excessive insulin release and hyperinsulinism whereas increased K_ATP channel activity leads to lower insulin secretion and diabetes. Paradoxically, mice with genetic deletion of K_ATP channels, or loss-of-function mutations, are only transiently hypoglycaemic during the neonatal period and often display reduced glucose-stimulated insulin secretion subsequently. Mice with K_ATP channel gain-of-function mutations are hyperglycaemic and have impaired glucose-stimulated insulin secretion, a phenotype that accurately mimics human diabetes. This review discusses how mice expressing altered K_ATP channels have provided valuable insight into β-cell function.