Survival of isolated human islets of Langerhans maintained in tissue culture

Importance of multiple endocrine cell types in islet organoids for type 1 diabetes treatment

Almost 50 years ago, scientists developed the bi-hormonal abnormality hypothesis, stating that diabetes is not caused merely by the impaired insulin signaling. Instead, the presence of inappropriate level of glucagon is a prerequisite for the development of type 1 diabetes (T1D). It is widely understood that the hormones insulin and glucagon, secreted by healthy β and α cells respectively, operate in a negative feedback loop to maintain the body's blood sugar levels. Despite this fact, traditional T1D treatments rely solely on exogenous insulin injections. Furthermore, research on cell-based therapies and stem-cell derived tissues tends to focus on the replacement of β cells alone. In vivo, the pancreas is made up of 4 major endocrine cell types, that is, insulin-producing β cells, glucagon-producing α cells, somatostatin-producing δ cells, and pancreatic polypeptide-producing γ cells. These distinct cell types are involved synergistically in regulating islet functions. Therefore, it is necessary to produce a pancreatic islet organoid in vitro consisting of all these cell types that adequately replaces the function of the native islets. In this review, we describe the unique function of each pancreatic endocrine cell type and their interactions contributing to the maintenance of normoglycemia. Furthermore, we detail current sources of whole islets and techniques for their long-term expansion and culture. In addition, we highlight a vast potential of the pancreatic islet organoids for transplantation and diabetes research along with updated new approaches for successful transplantation using stem cell-derived islet organoids.

The challenge of correctly reporting hormones content and secretion in isolated human islets

Background

An increased access of research laboratories to isolated human islets has improved our understanding of the biology of the endocrine pancreas and hence the mechanisms causing diabetes. However, in vitro studies of human islets remain technically challenging, and optimal use of such precious material requires a minimum of rigor and coordination to optimize the reliability and share of the information. A detailed report of the demographics of pancreas donors and of the procedures of islet handling after isolation is important but insufficient. Correct characterization of islet basic functions (a token of quality) at the time of experimentation is also crucial.

Scope of review

I have analyzed the literature reporting measurements of insulin and glucagon in the human pancreas or isolated human islets. The published information is often fragmentary. Elementary features such as islet size, insulin content, or rate of hormone secretion are either unreported or incorrectly reported in many papers. Although internal comparisons between control and test groups may remain valid, comparisons with data from other laboratories are problematic. The drawbacks, pitfalls and errors of common ways of expressing hormone content or secretion rates are discussed and alternatives to harmonize data presentation are proposed.

Major Conclusions

Greater coherence and rigor in the report of in vitro studies using human islets are necessary to ensure optimal progress in our understanding of the pathogenesis of diabetes.

Integration of mesenchymal stem cells into islet cell spheroids improves long-term viability, but not islet function

Pancreatic islets, especially the large islets (> 150µm in diameter) have poor survival rates in culture. Co-culturing with mesenchymal stem cells (MSCs) has been shown to improve islet survival and function. However, most co-culture studies have been comprised of MSC surrounding islets in the media. The purpose of this study was to determine whether islet survival and function was improved when the 2 populations of cells were intermingled with each other in a defined geometry. Hybrid spheroids containing 25, 50 or 75 or 90% islets cells with appropriate numbers of MSCs were created along with spheroids comprised of only islet cells or only MSCs. Spheroids were tested for yield, viability, diameter, cellular composition, and glucose-stimulated insulin secretion. The 25% islet/75% MSC group created the fewest spheroids, with the poorest survival and insulin secretion and the largest diameter. The remaining groups were highly viable with average diameters under 80µm at formation. However, the hybrid spheroid groups preferred to cluster in islet-only spheroids. The 50, 75 and 90% islet cell groups had excellent long-term survival with 90-95% viability at 2 weeks in culture, compared with the islet only group that were below 80% viability. The glucose-stimulated insulin secretion was not statistically different for the 50, 75, or 90 groups when exposed to 2.4, 16.8, or 22.4 mM glucose. Only the spheroids with 25% islet cells had a statistically lower levels of insulin release, and the 100% had statistically higher levels at 22.4 mM glucose and in response to secretagogue. Thus, imbedded co-culture improved long-term viability, but failed to enhance glucose-stimulated insulin secretion in vitro.

Islet Cell Transplantation: In Vivo and in Vitro Functional Assessment of Nonhuman Primate Pancreatic Islets

Transplantation of pancreatic islets of Langerhans as a therapeutic approach for treatment of type I diabetes offers an alternative to subcutaneous insulin injections. Normalization of blood glucose levels by transplanted islets may prevent the development of diabetes-related complications. Problems related to rejection, recurrence of autoimmunity, and local inflammation upon transplantation of islets into the liver need to be solved before the implementation of islet cell transplantation can be viewed as a justifiable procedure in a large cohort of patients. Islet cell isolation has been quite successful in small animals, but the translation of this approach to nonhuman primates has been less rewarding. One of the main problems encountered in nonhuman primate models is the difficulty of isolating an adequate number of functional islets for transplantation. The aim of the present study was to develop a method for isolating a sufficient number of viable islets from nonhuman primates to allow for reversal of diabetes. By implementing minor modifications in the automated method for human islet isolation we were able to obtain viable, functional islets that responded normally to glucose stimulation in vitro. These islets were also able to reverse diabetes in immunocompromised nude mice, rendered diabetic by streptozotocin. This method of islet cell isolation has enabled us to proceed with protocols of allogeneic islet cell transplantation in preclinical, nonhuman primate models.

Long-term cryopreservation of reaggregated pancreatic islets resulting in successful transplantation in rats

Preservation of pancreatic islets for long-term storage of islets used for transplantation or research has long been a goal. Unfortunately, few studies on long-term islet cryopreservation (1 month and longer) have reported positive outcomes in terms of islet yield, survival and function. In general, single cells have been shown to tolerate the cryopreservation procedure better than tissues/multicellular structures like islets. Thus, we optimized a method to cryopreserve single islet cells and, after thawing, reaggregated them into islet spheroids. Cryopreserved (CP) single human islet cells formed spheroids efficiently within 3-5 days after thawing. Approximately 79% of islet cells were recovered following the single-cell cryopreservation protocol. Viability after long-term cryopreservation (4 weeks or more) was significantly higher in the CP islet cell spheroids (97.4 ± 0.4%) compared to CP native islets (14.6 ± 0.4%). Moreover, CP islet cell spheroids had excellent viability even after weeks in culture (88.5 ± 1.6%). Metabolic activity was 4-5 times higher in CP islet cell spheroids than CP native islets at 24 and 48 h after thawing. Diabetic rats transplanted with CP islet cell spheroids were normoglycemic for 10 months, identical to diabetic rats transplanted with fresh islets. However, the animals receiving fresh islets required a higher volume of transplanted tissue to achieve normoglycemia compared to those transplanted with CP islet cell spheroids. By cryopreserving single cells instead of intact islets, we achieved highly viable and functional islets after thawing that required lower tissue volumes to reverse diabetes in rats.

Clinical Islet Isolation

The overarching success of islet transplantation relies on the success in the laboratory to isolate the islets. This chapter focuses on the processes of human islet cell isolation and the ways to optimally provide islet cells for transplantation. The major improvements in regards to the choice of enzyme type, way the digested pancreas tissue is handled to best separate islets from the acinar and surrounding tissues, the various methods of purification of the islets, their subsequent culture and quality assurance to improve outcomes to culminate in safe and effective islet transplantation will be discussed. After decades of improvements, islet cell isolation and transplantation now clearly offer a safe, effective and feasible therapeutic treatment option for an increasing number of patients suffering from type 1 diabetes specifically for those with severe hypoglycaemic unawareness.

Krüppel-Like Factor 4 Overexpression Initiates a Mesenchymal-to-Epithelial Transition and Redifferentiation of Human Pancreatic Cells following Expansion in Long Term Adherent Culture

A replenishable source of insulin-producing cells has the potential to cure type 1 diabetes. Attempts to culture and expand pancreatic β-cells in vitro have resulted in their transition from insulin-producing epithelial cells to mesenchymal stromal cells (MSCs) with high proliferative capacity but devoid of any hormone production. The aim of this study was to determine whether the transcription factor Krüppel-like factor 4 (KLF4), could induce a mesenchymal-to-epithelial transition (MET) of the cultured cells. Islet-enriched pancreatic cells, allowed to dedifferentiate and expand in adherent cell culture, were transduced with an adenovirus containing KLF4 (Ad-Klf4). Cells were subsequently analysed for changes in cell morphology by light microscopy, and for the presence of epithelial and pancreatic markers by immunocytochemistry and quantitative RT/PCR. Infection with Ad-Klf4 resulted in morphological changes, down-regulation of mesenchymal markers, and re-expression of both epithelial and pancreatic cell markers including insulin and transcription factors specific to β-cells. This effect was further enhanced by culturing cells in suspension. However, the effects of Ad-KLf4 were transient and this was shown to be due to increased apoptosis in Klf4-expressing cells. Klf4 has been recently identified as a pioneer factor with the ability to modulate the structure of chromatin and enhance reprogramming/transdifferentiation. Our results show that Klf4 may have a role in the redifferentiation of expanded pancreatic cells in culture, but before this can be achieved the off-target effects that result in increased apoptosis would need to be overcome.

DCD for Islet Transplantation

Pancreatic islet transplantation has the potential to become the most physiologically advantageous and minimally invasive procedure for the treatment of type 1 diabetes mellitus. Since the first clinical islet transplantation was performed at the University of Minnesota in 1974 [1], the results have been far from ideal for more than two decades in spite of an improvement of islet isolation technique by Ricordi et al. [2–4]. The introduction of the Edmonton protocol, with a highly improved rate of insulin independency, encouraged us to promote clinical islet transplantation [5, 6]. In Japan, we organized the Working Group (The Japanese Islet Transplant Registry) in 1997 under the Japanese Society for Pancreas and Islet Transplantation for the purpose of starting clinical islet transplantation. The first issue of the Working Group was to construct a system of clinical islet transplantation in Japan including the registration of the recipients, procurement of the pancreas for islet isolation and transplantation of the isolated islets. In Japan, afterwards, various problems facing to a start of clinical islet transplantation have been discussed and we completed the guideline for clinical islet transplantation in Japan. The Japanese Organ Transplant Law was enforced in 1997 and organ transplantations using brain dead (DBD) donors were finally started. Since the islet transplantation was not included in the Japanese Organ Transplant Law because it was categorized as tissue transplantation, we were able to use the pancreas only from DCD donors for islet transplantation. The first islet isolation from the human pancreas was performed in 2003.9 and the first islet transplantation was performed in 2004.4 [7–9]. Sixty-five islet isolations and 34 islet transplantations were performed in our country from 2003.9.12 to 2007.3.11 [10].

In this chapter, we describe the current status of clinical islet transplantation using DCD donors in Japan.

Amyloid in the islets of Langerhans: thoughts and some historical aspects

Deposition of amyloid, derived from the polypeptide hormone islet amyloid polypeptide (IAPP; 'amylin') is the single most typical islet alteration in type 2 diabetes. Islet amyloid was described as hyalinization already in 1901, but not until 1986 was it understood that it is a polymerization product of a novel β-cell regulatory product. The subject of this focused review deals with the pathogenesis and importance of the islet amyloid itself, not with the biological effect of the polypeptide. Similar to the situation in Alzheimer's disease, it has been argued that the amyloid may not be of importance since there is no strict correlation between the degree of islet amyloid infiltration and the disease. However, it is hardly discussable that the amyloid is important in subjects where islets have been destroyed by pronounced islet amyloid deposits. Even when there is less islet amyloid the deposits are widely spread, and β-cells show ultrastructural signs of cell membrane destruction. It is suggested that type 2 diabetes is heterogeneous and that in one major subtype aggregation of IAPP into amyloid fibrils is determining the progressive loss of β-cells. Interestingly, development of islet amyloid may be an important event in the loss of β-cell function after islet transplantation into type 1 diabetic subjects.

Low-temperature preservation of isolated islets is superior to conventional islet culture before islet transplantation

BACKGROUND

Although culturing islets before transplantation provides flexibility for evaluation of isolated islets and pretreatment of patients, it is well-known that isolated islets deteriorate rapidly in culture. In this study, we evaluated optimal temperature for culture/preservation of isolated human islets before transplantation.

METHODS

Isolated islets were cultured or preserved for 48 hr in the following culture/preservation conditions: preservation at 4 degrees C in University of Wisconsin solution and culture at 22 degrees C or 37 degrees C in culture medium.

RESULTS

Islet morphology after 4 degrees C preservation was similar to that of fresh islets, whereas islet diameter after 37 degrees C or 22 degrees C culture was smaller than that of fresh islets. Islet yield significantly decreased at higher temperatures (24% loss in 37 degrees C culture and 19% loss in 22 degrees C culture, but <5% loss in 4 degrees C preservation). Cultured/preserved islets were transplanted into diabetic nude mice. The attainability of posttransplantation normoglycemia was significantly higher in the 4 degrees C preservation group than in 22 degrees C and 37 degrees C culture groups.

CONCLUSION

Preservation of isolated islets at 4 degrees C improves the outcome of islet transplantation more efficiently than preservation at 22 degrees C or 37 degrees C. Based on these data, we have performed short-time cold storage of isolated islets instead of culturing for current clinical islet transplantation.

Risk factors for islet loss during culture prior to transplantation

Culturing islets can add great flexibility to a clinical islet transplant program. However, a reduction in the islet mass has been frequently observed during culture and its degree varies. The aim of this study was to identify the risk factors associated with a significant islet loss during culture. One-hundred and four islet preparations cultured in an attempt to use for transplantation constituted this study. After culture for 20 h (median), islet yield significantly decreased from 363 309 +/- 12 647 to 313 035 +/- 10 862 islet equivalent yield (IE) (mean +/- SE), accompanied by a reduction in packed tissue volume from 3.9 +/- 0.1 to 3.0 +/- 0.1 ml and islet index (IE/islet particle count) from 1.20 +/- 0.04 to 1.05 +/- 0.04. Culture did not markedly alter islet purity or percent of trapped islet. Morphology score and viability were significantly improved after culture. Of 104 islet preparations, 37 suffered a substantial islet loss (> 20%) over culture. Factors significantly associated with risk of islet loss identified by univariate analysis were longer cold ischemia time, two-layer method (TLM) preservation, lower islet purity, and higher islet index. Multivariate analysis revealed that independent predictors of islet loss were higher islet index and the use of TLM. This study provides novel information on the link between donor- isolation factors and islet loss during culture.

Anatomical and histological observation on the pancreas in adult zebrafish

OBJECTIVES

To investigate the anatomic structure of the pancreas and the distribution of the islets in adult zebrafish.

METHODS

In situ immunofluorescent staining, electron microscopy, and serial paraffin-embedded sectioning with hematoxylin/eosin staining were applied.

RESULTS

The pancreas along the intestine included 4 relatively independent and concentrated lobes, in which 4 kinds of islets-principal islets, Brockmann bodies, diffusely existing islets, and single beta-cell-were observed. Some islets contained both alpha and beta cells, whereas some contained only beta cells. The islet number in each adult zebrafish averaged 84.53 +/- 43.77; and the lower quartile, median, and upper quartile were 55.25, 70.50, and 112.00, respectively (n = 40). The different islets were differently distributed in the 4 pancreatic lobes with statistical significance (P < 0.05). Meanwhile, 3 kinds of secretory granules were found in the cytoplasm of different islet cells.

CONCLUSIONS

According to the distinct distribution, concentration of the pancreas, and different contents of the islets within the pancreas, 4 lobes of the pancreas along the intestine-the gallbladder-spleen lobe, the middle lobe, the left lobe, and the ventral lobe-were identified in adult zebrafish.

Nutrient control of insulin secretion in isolated normal human islets

Pancreatic islets were isolated from 16 nondiabetic organ donors and, after culture for approximately 2 days in 5 mmol/l glucose, were perifused to characterize nutrient-induced insulin secretion in human islets. Stepwise increases from 0 to 30 mmol/l glucose (eight 30-min steps) evoked concentration-dependent insulin secretion with a threshold at 3-4 mmol/l glucose, K(m) at 6.5 mmol/l glucose, and V(max) at 15 mmol/l glucose. An increase from 1 to 15 mmol/l glucose induced biphasic insulin secretion with a prominent first phase (peak increase of approximately 18-fold) and a sustained, flat second phase ( approximately 10-fold increase), which were both potentiated by forskolin. The central role of ATP-sensitive K(+) channels in the response to glucose was established by abrogation of insulin secretion by diazoxide and reversible restoration by tolbutamide. Depolarization with tolbutamide or KCl (plus diazoxide) triggered rapid insulin secretion in 1 mmol/l glucose. Subsequent application of 15 mmol/l glucose further increased insulin secretion, showing that the amplifying pathway is operative. In control medium, glutamine alone was ineffective, but its combination with leucine or nonmetabolized 2-amino-bicyclo [2,2,1]-heptane-2-carboxylic acid (BCH) evoked rapid insulin secretion. The effect of BCH was larger in low glucose than in high glucose. In contrast, the insulin secretion response to arginine or a mixture of four amino acids was potentiated by glucose or tolbutamide. Palmitate slightly augmented insulin secretion only at the supraphysiological palmitate-to-albumin ratio of 5. Inosine and membrane-permeant analogs of pyruvate, glutamate, or succinate increased insulin secretion in 3 and 10 mmol/l glucose, whereas lactate and pyruvate had no effect. In conclusion, nutrient-induced insulin secretion in normal human islets is larger than often reported. Its characteristics are globally similar to those of insulin secretion by rodent islets, with both triggering and amplifying pathways. The pattern of the biphasic response to glucose is superimposable on that in mouse islets, but the concentration-response curve is shifted to the left, and various nutrients, in particular amino acids, influence insulin secretion within the physiological range of glucose concentrations.

Islet graft assessment in the Edmonton Protocol: implications for predicting long-term clinical outcome

The success of the Edmonton Protocol for islet transplantation has provided new hope in the treatment of type 1 diabetes. This study reports on the assessment of 83 human islet grafts transplanted using the Edmonton Protocol since 1999. Cellular composition, as assessed by immunohistochemistry, showed a lower islet purity (approximately 40%) than has been reported in previous studies using dithizone staining to quantitate islet equivalents. Furthermore, grafts were found to contain substantial populations of exocrine and ductal tissue. Total cellular insulin transplanted was 8,097.6 +/- 3,164.4 microg/patient, and was significantly lower in bottom gradient layer grafts than top gradient layer or whole/combined grafts (P < 0.0005). A static incubation test for islet function gave a stimulation index of 3-4, although this measure did not correlate with posttransplant metabolic outcome. Furthermore, we confirmed a previously reported trend in which donor age affects islet yield and purity. It is important to note that a significant positive correlation was observed between the number of islet progenitor (ductal-epithelial) cells transplanted and long-term metabolic success as assessed an by intravenous glucose tolerance test at approximately 2 years posttransplant. In summary, careful assessment of islet graft composition is needed in a clinical transplantation program to accurately estimate islet purity and assess the contribution of other cell types present, such as islet progenitor cells.

Non-heart-beating organ donors: a potential source of islets for transplantation?

BACKGROUND

The shortage of organ donors relative to the number of patients on transplant waiting lists has led to a renewed interest in the use of non-heart-beating (NHB) organ donors in many centers. The lack of donors is also a problem for islet transplantation. The disparity between donor organs and potential recipients is further exacerbated by the requirement to transplant a large number of islets to increase the chance of success and the high level of variability in islet isolation yield. Non-heart-beating (NHB) donors have not previously been assessed as a source of islets for transplantation, and it is unknown what affects the additional factor of warm ischemic injury associated with NHB organs may have on the success of islet isolation.

METHODS

This study assesses the yield and function of islets from NHB donors and compares the results with islets obtained from heart-beating brain-dead (HB) donors.

RESULTS

There were no differences in the yield of islets per gram of pancreas, 1788 (0-4620) NHB vs. 1580 (26-2544) HB (median, range). The secretory function was also similar in both groups, with stimulation indices of 0.71-3.49 for NHB vs. 0.30-3.57 for HB (overall range). There was no correlation between islet yield and warm ischemia time in the NHB donor group.

CONCLUSIONS

In conclusion, the study has demonstrated that it is possible to isolate large numbers of islets from NHB donor pancreata and that, where NHB donor programs exist, these could provide a significant addition to the number of potentially transplantable islets.

Effect of high glucose concentration on proinsulin biosynthesis and conversion by human islets

In the present study we investigate whether glucose concentration could have an effect on proinsulin biosynthesis and processing. We cultured control human islets under chronic high and low glucose concentrations. After the culture period, islets were pulse-labeled and chased for different periods of time. Proteins from islets were collected, insulin immunoprecipitated, and analyzed by alkaline-urea gel electrophoresis. We have found an accelerated rate of proinsulin conversion by those islets exposed to high glucose concentration (at 24.4 mM of glucose), but not by those islets cultured at low glucose concentration (at 5.5 mM of glucose). However, we do not observe any decrease or increase on newly proinsulin synthesis in any of these conditions.

Effect of pancreatic warm ischemia on islet yield and viability in dogs

BACKGROUND

Defining tolerable warm ischemia (WI) is mandatory before nonheartbeating cadavers can be used to enlarge the donor pool. No studies to date have precisely evaluated the effect of pancreatic WI on islet yield and viability in a large animal model.

METHODS

We used mongrel dogs in our study at the University of Minnesota. Excised pancreases were left in situ for a designated period (0, 30, 45, and 60 min in groups 1 to 4, respectively) of WI. Then, they were digested by the automated collagenase digestion method of Ricordi, purified on Euro-Ficoll discontinuous gradients with the COBE cell processor, and autotransplanted into the liver via a mesenteric vein. We compared the four groups in terms of islet yield, expressed as islet equivalents (IE; diameter standardizing to 150 microm) per pancreas weight (IE/g pancreas), and viability, assessed by functional success (maintenance of normoglycemia for 2 weeks) after transplant.

RESULTS

Mean islet yield (+/- SD) and the functional success rate after transplant were as follows: 6200+/-1800 IE/g pancreas and 4 of 4 (100%) in group 1; 6300+/-4400 and 4 of 4 (100%) in group 2; 3800+/-2600 and 2 of 4 (50%) in group 3; and 1400+/-1300 and 0 of 4 (0%) in group 4 (P=0.01 vs. group 1).

CONCLUSIONS

With 30 min or less of WI, there are no deleterious effects on islet yield and viability. However, with periods of WI longer than 30 min, the loss in islet yield is severe, resulting in functional failure after autotransplantation. The limit of WI that is tolerable for islets is shorter than for a whole pancreas.

Enzymatic, metabolic and secretory patterns in human islets of type 2 (non-insulin-dependent) diabetic patients

Islets were isolated by automatic digestion from non-diabetic cadaveric organ donors and from Type 2 (non-insulin-dependent) diabetic subjects. The activity of FAD-glycerophosphate dehydrogenase, but not that of either glutamate dehydrogenase, glutamate-oxalacetate transaminase or glutamate-pyruvate transaminase, was lower in Type 2 diabetic patients than control subjects. Hexokinase, glucokinase and glutamate decarboxylase activities were also measured in islets from control subjects. The utilization of D-[5-3H]glucose, oxidation of D-[6-14C]glucose and release of insulin evoked by D-glucose were all lower in Type 2 diabetic patients than control subjects. The secretory response to the combination of L-leucine and L-glutamine appeared less severely affected. Islets from Type 2 diabetic patients may thus display enzymatic, metabolic and secretory anomalies similar to those often observed in animal models of Type 2 diabetes, including a deficiency of beta-cell FAD-linked glycerophosphate dehydrogenase, the key enzyme of the glycerol phosphate shuttle.

Regulation of insulin release in persistent hyperinsulinaemic hypoglycaemia of infancy studied in long-term culture of pancreatic tissue

Pancreatic tissue was obtained during therapeutic subtotal pancreatectomy from five infants with persistent hyperinsulinaemic hypoglycaemia of infancy (so-called nesidioblastosis). Collagenase digests of the specimens were cultured in RPMI 1640 medium on extracellular matrix-coated plates. Acute insulin secretion showed minimal sensitivity to changes in glucose concentration. Sensitivity to other nutrient secretagogues such as glyceraldehyde, leucine, alpha-ketoisocaproic acid and arginine was variable, showing either diminished or absent response. On the other hand, stimulators of Beta cell cAMP and modulators of the phosphoinositide-protein kinase C pathway were effective inducers of insulin release. The response to cAMP stimulators was independent of the glucose concentration. Although insulin output was high in the absence of glucose, this was not due to passive leak of hormone, since both removal of calcium and addition of somatostatin and epinephrine inhibited the secretion. Beta cells were more sensitive to somatostatin than epinephrine; however, both agents failed to completely suppress the release even at suprapharmacological concentrations. Although it cannot be excluded that the culture conditions affected Beta cell function, the present findings may suggest that cultured Beta cells in persistent hyperinsulinaemic hypoglycaemia of infancy behave like fetal Beta cells at early developmental stages.

Islet isolation assessment in man and large animals

Recent progress in islet isolation from the pancreas of large mammals including man, accentuated the need for the development of precise and reproducible techniques to assess islet yield. In this report both quantitative and qualitative criteria for islet isolation assessment were discussed, the main topics being the determination of number, volume, purity, morphologic integrity and in vitro and in vivo function tests of the final islet preparations. It has been recommended that dithizone should be used as a specific stain for immediate detection of islet tissue making it possible to estimate both the total number of islets (dividing them into classes of 50 mu diameter range increments) and the purity of the final preparation. Appropriate morphological assessment should include confirmation of islet identification, assessment of the morphological integrity and of the purity of the islet preparation. The use of fluorometric inclusion and exclusion dyes together have been suggested as a viability assay to simultaneously quantitate the proportion of cells that are intact or damaged. Perifusion of islets with glucose provides a dynamic profile of glucose-mediated insulin release and of the ability of the cells to down regulate insulin secretion after the glycemic challenge is interrupted. Although perifusion data provides a useful guide to islet viability the quantity and kinetics of insulin release do not necessarily predict islet performance after implantation. Therefore, the ultimate test of islet viability is their function after transplantation into a diabetic recipient. For this reason, in vivo models of transplantation of an aliquot of the final islet preparation into diabetic nude (athymic) rodents have been suggested. We hope that these general guidelines will be of assistance to standardize the assessment of islet isolations, making it possible to better interpret and compare procedures from different centers.

Studies on insulin secretion by monolayer cultures of normal and tumorous human pancreatic cells. Effects of glucose, somatostatin and SMS 201-995

Recently, somatostatin analogs have been introduced which can be used clinically in the treatment of tumorous or functional hypoglycemia. In the present study we investigated in vitro the regulation, the degree of autonomy and the sensitivity to natural somatostatin and its analog SMS 201-995 of insulin secretion by monolayer cultures of human pancreatic cells obtained from patients with insulinomas and from a newborn with nesidioblastosis. All cultures released insulin upon the addition of dibutyryl-cAMP and calcium, demonstrating their intact viability. Insulin secretion from nontumorous pancreatic cells surrounding an insulinoma was dose-dependently stimulated by glucose. In contrast, insulin release by B cells from a patient with nesidioblastosis and from 2 insulinomas was not stimulated by the addition of glucose. Native somatostatin (SRIF) and the synthetic analog SMS 201-995 inhibited insulin secretion from all cultures. The inhibitory effects of SRIF and SMS in the culture from the nesidioblastosis tissue, could be reversed by the addition of 11.2 mmol glucose/l, but not in one of the insulinoma cultures. This demonstrates that some sensitivity to glucose is present in B cells from the nesidioblastosis tissue, despite the unresponsiveness to glucose alone. Insulin release by insulinoma cells was blocked by somatostatin, while it was inhibited to some extent only in the cultures of nontumor B cells and of cells from the nesidioblastosis tissue. In conclusion, it was shown that insulin release by the cultured B cells obtained from several pathological conditions differed with regard to the autonomy of hormone release (glucose sensitivity) and the sensitivity to somatostatin and its analog.

Insulin secretion from perifused rat pancreatic pseudoislets

Isolated adult rat pancreatic islets were dispersed into single cells and cultured free-floating for 3 to 4 d, during which time islet cells reaggregated spontaneously into spherical clusters or pseudoislets. The gross morphology of these tissues resembled nondissociated islets. Electron microscopy revealed well-preserved cell ultrastructure and intercellular membrane connections. Immunofluorescent localization of islet cell types showed that A cells tended to be peripherally distributed around a B cell core, with D cells scattered throughout the aggregate mass. The dynamics of insulin release from pseudoislets were evaluated in vitro by perifusion techniques. Pseudoislets exhibited clear biphasic dose-dependent insulin responses to 30 min glucose stimulation over the range 5.5 to 30 mM. Repeated 2-min pulses with 22 mM glucose elicited brief monophasic spikes of insulin release of consistent magnitude. L-Arginine (5 to 20 mM) evoked biphasic insulin release but these responses were not dose-dependent. These data indicate that islet cells reaggregate into structures with close morphologic similarities to intact islets, and that pseudoislet B cells continue to secrete insulin in response to nutrient secretagogues, comparable to that seen with islets in vitro and in situ.

Properties of isolated human islets of Langerhans: insulin secretion, glucose oxidation and protein phosphorylation

In the present study, human islets were isolated by collagenase digestion from the pancreases of three kidney donors. Maintainance of the islets in tissue culture enabled insulin release, glucose oxidation and Ca2+ -calmodulin-dependent protein phosphorylation to be determined using the same islets. Increasing glucose over a range 0-20 mmol/l resulted in a sigmoidal stimulation of insulin release (28.8 +/- 5.2 to 118.4 +/- 25.8 microU . islet-1 . h-1, n = 10; threshold less than 4 mmol/l). There was a marked correlation between the insulin secretory response of the islets to glucose and their rate of glucose oxidation (5.9 +/- 0.3 at glucose 2 mmol/l up to 25.8 +/- 1.8 pmol . islet-1 . h-1 at 20 mmol/l, r = 0.98). N-acetylglucosamine (20 mmol/l) failed to elicit a secretory response from the islets. Stimulation of insulin secretion by glucose was dependent upon the presence of extracellular Ca2+. Extracts of the islets contained a Ca2+ -calmodulin-dependent protein kinase which phosphorylated a 48-kdalton endogenous polypeptide. Myosin light-chain kinase activity was demonstrated in the presence of exogenous myosin light chains. This report demonstrates for the first time the sigmoidal nature of glucose-stimulated insulin release from isolated human islets, and its correlation with enhanced glucose oxidation. Furthermore, this is the first report of the presence of Ca2+ -dependent protein kinases in human islets.

Morphological investigations into the structure of frozen-thawed rat islets of Langerhans

Fetal rat pancreases, cultured for 8 days in RPMI 1640, were successively frozen to -196 degrees C. The samples, defrosted at different intervals (0, 5, 1, 2, 7, and 15 days), were examined by TEM and SEM. The effects of culture, various cooling times, warming rates, thawing procedures, dimethyl sulfoxide concentration, and ultrastructural features of cellular elements were analyzed.

Organ explant culture of adult Syrian golden hamster pancreas

An organ explant culture system has been developed for long term maintenance of adult pancreatic tissue from the Syrian golden hamster. Gastric and duodenal lobe explants of up to 0.5 cm2 size were placed in tissue culture dishes (60 mm2) on Gelfoam sponge rafts to which was added 5 ml of CMRL medium 1066 supplemented with heat inactivated newborn bovine serum, L-glutamine, hydrocortisone, insulin, and antibiotics. Dishes were placed in a controlled atmosphere chamber, which was gassed with 45% O2, 50% N2, and 5% CO2 and incubated at 36.5 degrees C. Viability of the tissues was determined by light and electron microscopy as well as by [3]thymidine incorporation. Explants were viable for up to 70 d. Zymogen granule-containing cells characteristic of acinar cells and mucus-containing cells characteristic of ductal cells were present throughout this period. However, endocrine cells were only present for the 1st wk in culture.

Murine islet cryopreservation and corticosteroids: functional studies

Knowledge of protective effects of corticosteroids on traumatized cells prompted us to test the potential benefit of islet cryopreservation in the presence of hydrocortisone. Neonatal murine islets were isolated by collagenase, followed by 2- to 3-day tissue culture. Precryopreservation glucose-stimulated (50-500 mg/dl) insulin release was 25-388% above basal (mean = 113%) in 18/20 fresh islet preparations. Subsequent freezing was done in RPMI 1640 medium plus 10% (v/v) heat-inactivated fetal calf serum and 10% (v/v) Me2SO with or without 1 mg/ml hydrocortisone at 0.25 degrees C per minute in a programmed freezing system, to -80 degrees C, and stored for greater than 60 days at -196 degrees C. Thawing, by transfer to room air, was followed by dilution, 4x (v/v), in 4 degrees C RPMI plus 10% protein, after which glucose-stimulated insulin release was reassessed, showing 56-280% response over basal in 3/8 steroid-treated preparation and 20-220% response in 3/10 control preparations. Basal insulin release was 0.72 ng/microgram protein/hr in fresh islets (N = 20) and 0.22 ng/microgram protein/hr after freeze-thawing. We conclude that functional islet survival by this method is approximately 30% and that hydrocortisone did not improve viability.

Cell culture and in vitro studies of fresh and cryopreserved human insulinoma

Dispersed cells from both fresh and cryopreserved human insulinoma have been maintained in cell culture. Initial yield of viable cells was 50% for fresh and 25% for cryopreserved tissue. Viability of cells in culture was documented by increasing numbers of cells (doubling time approximately 5 d initially and 2 d at the sixth subculture for both fresh and cryopreserved tissue) and continued release of insulin over time (approximately 100 ng/ml per 10(5) cells at 10 d and 175 ng/ml per 10(5) cells at 30 d of culture for both fresh and cryopreserved tissue). Evidence that cells growing in culture were beta cells was provided by: (a) recovery of intracellular and extracellular immunoreactive insulin (IRI), (b) electron microscopic morphology, and (c) immunohistochemical staining. Cells from fresh insulinoma incubated with increasing concentrations of extracellular glucose released increasing amounts of IRI up to approximately 15 mM glucose, which paralleled changes in plasma insulin obtained during a preoperative glucose tolerance test.

Short- and long-term effects of dimethyl sulfoxide on mouse pancreatic islet B-cell function in vitro

Dimethylsulfoxide has been used as a cryoprotectant for the endocrine pancreas. To explore possible harmful effects of Me2SO influenced neither glucose-stimulated insulin release, nor islet glucose oxidation. On the other hand, 1 M but not 0.25 M Me2SO decreased glucose-stimulated (pro)insulin and total protein biosynthesis in acute experiments. In islet culture experiments with Me2SO-supplemented culture media there was no obvious effects on glucose-stimulated (pro)insulin biosynthesis. It is suggested that Me2SO in the range 0.01-0.5 M does not affect islet B-cell function in vitro.

Nesidioblastosis of the pancreas: definition of the syndrome and the management of the severe neonatal hyperinsulinaemic hypoglycaemia

Three newborn infants are reported who developed severe non-ketotic hypoglycaemia (blood glucose less than 1.1 mmol/l; 19.8 mg/100 ml) within 6 hours of birth. All had inappropriately raised plasma insulin concentrations for the level of glycaemia, and required high rates of glucose infusion (less than 15 mg glucose/kg per minute) to prevent symptoms of hypoglycaemia. Medical treatment (hydrocortisone, diazoxide, chlorothiazide, phenytoin, propranolol, and depot glucagon) was ineffective in preventing hypoglycaemia and all 3 infants were subjected to partial and then total pancreatectomy. The pathological features of nesidioblastosis are reported from quantitative immunohistochemical studies on the pancreata. These results together with those from metabolic and endocrine studies performed on the 3 infants during the investigation of the cause of the hypoglycaemia and during the preoperative and postoperative period are presented in detail in order to define a practical approach to the management of this difficult clinical problem in the neonate.

Glucagon production by cultured pancreatic islets: effects of different culture conditions and media

Various conditions for tissue culture of collagenase-isolated mouse pancreatic islets were studied for their effects on the glucagon production of the cultured specimens. Culture media containing heat-treated bovine calf serum degraded [125I]glucagon to a much less extent than those supplemented with untreated serum. Addition of aprotinin to the heat-treated serum gave a further reduction of the [125I]glucagon degradation in the culture medium. A similar supplementation of Medium 199, used for culture of isolated islets, resulted in the most extensive glucagon accumulation in the culture medium. Islets cultured free-floating or attached to the bottom of the culture dishes contained similar amounts of glucagon. However, the free-floating islets released less glucagon when tested in short-term experiments performed at the end of the 1 wk culture period. A comparison between different culture media showed that islets cultured in RPMI-1640 had the highest glucagon content and released most glucagon to the culture medium. Moreover, these islets responded most actively to an acute arginine challenge at the end of the culture period. The present data suggest that the optimal conditions for culture of isolated islets aimed at studies of glucagon production may be obtained by using a culture medium consisting of RPMI-1640 supplemented with both a proteinase inhibitor and heat-inactivated serum.

Pancreas and islet transplantation. II. Clinical trials

Clinical islet allotransplantation has been a safe, but largely unsuccessful enterprise. It has been difficult to apply techniques that might overcome the islet yield and allograft rejection problems encountered in animal experiments. Over the past decade only 4 of 74 attempts at islet transplantation have been followed by long term withdrawal of exogenous insulin therapy, and there are problems with intrepretation of the outcome in each of theses cases, as discussed in the preceding section. In the islet allograft situation, the failures may have been for technical or for immunological reasons. In the autograft situation, rejection could not occur and the failures were clearly technical. The success rate with islet autografts gives some indication as to what might be achieved with islet allotransplantation if rejection could be prevented in the latter situation. The islet autotransplant experience is not entirely predictative, however, for two reasons: 1) the uncertainty over the contribution of the pancreatic remnant to carbohydrate metabolism when less than the total pancreatectomy is done; 2) the increased difficulty with liberating islets from diseased, fibrotic pancreases. For both islet allo- and autotransplantation, the success rate will probably remain low until more effective techniques are developed for preparation of islets from adult pancreases. For the allograft situation, additional advances will be needed in immunosuppression or in techniques to alter islet graft immunogenicity in order to overcome the rejection phenomenon.

Insulin release from human pancreatic islets in vitro

Islets of Langerhans were isolated by collagenase digestion from the pancreas of a 39 year-old female renal transplant donor. The islets were subjected to three consecutive periods of tissue culture, after each of which they were incubated in vitro with various agents whose effects on insulin release from islets of laboratory animals have previously been established. After the first culture period, the basal insulin secretion rate of 5.2 microunits/islet/h seen with 2 mmol/l glucose was increased approx. 5-fold on raising the glucose concentration to 20 mmol/l. The islets retained the insulin-secretory response to 20 mmol/l glucose throughout the period of study. Insulin secretion was also stimulated by mannose, leucine, alpha-ketoisocaproate, dihydroxyacetone and 3-hydroxybutyrate, but not by fructose or N-acetyl-glucosamine. Fructose however increased insulin release in the presence of 4 mmol/l glucose. Caffeine elicited insulin release in the absence of glucose and enhanced insulin release in response to 10 mmol/l glucose. Glucose-stimulated insulin release was inhibited by trifluoperazine (25 mumol/l).

Organ culture of the Islets of Langerhans from young and senescent rats

The B-cells of the endocrine pancreas constitute an adequate model for in vitro study of the aging process in highly differentiated cells. In the present study, collagenase-isolated islets of Langerhans from young and senescent rats were cultured up to 28 days. The response of the B-cells to the stimulatory conditions of the culture medium involved the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, and secretory granules. Correlated data from light microscopy, electron microscopy, and insulin radioimmunoassay show that the differentiation and function of senescent B-cells are maintained in culture, as it has been proven for the B-cells of younger animals. On the other hand, signs of cytological deficiency not directly concerned with the specific function of B-cells were observed: abnormal mitochondria and lysosomes are more numerous in the senescent B-cells. The proliferative capacity of the B-cells of aged rats is reduced.

Cryogenic preservation of isolated rat Islets of Langerhans: effect of cooling and warming rates

Isolated rat Islets of Langerhans have been frozen to and stored at -196 degrees. After thawing, these islets were capable of secreting near normal levels of insulin in response to graded glucose challenge. Maximal retention of functional viability as measured by the ability of the islets to secrete insulin in response to a glucose challenge was obtained after freezing islets at a cooling rate of approximately 75 degrees per minute in the presence of 1.0 mol/1 dimethyl sulfoxol followed by warming at rates of greater than 3.5 degrees/minute. The critical freezing parameters include the time and temperature of exposure to dimethyl sulfoxide, the rate of cooling, the temperature of the post-thaw dilution from the freezing medium and the presence of serum in the dilution medium.

Preservation of beta cell function in adult human pancreatic islets for several months in vitro

Islets of Langerhans were isolated from four human kidney donors, aged 16 to 21 years by the collagenase method described for isolation of rodent islets. So far the human islets have been kept in tissue culture, without attachment, in medium RPMI 1640 supplemented with 10% calf serum for more than 9 months, with preservation of the ability to release insulin in response to glucose stimulation. Replacement of calf serum with serum from normal human subjects did not affect B-cell survival, but resulted in elevated insulin values partly due to lower insulin degrading activity. Thus the described technique presents a valuable tool for studying chronic effects of metabolites and hormones on islet function, as well as for islet storage prior to transplantation into humans.

Syngeneic transplantation of the fetal rat pancreas IV. Dissociated versus whole organ implantation

Reversal of insulinopenia, hyperglycemia, glycosuria, and polyuria associated with severe alloxan diabetes in the rat was accomplished by syngeneic transplantation of whole late-gestation fetal rat pancreata. Intravenous glucose tolerance test (GTT) revealed an improved yet still abnormal glucose and insulin response in reversed recipients reconstituted with as few as two pancreata from fetal donors. Eight fetal donors were sufficient to return glucose and insulin response following GTT to normal. Seventy to eighty percent fewer donors were required when the pancreata were transplanted in their entirely as opposed to transplantation of pancreata subjected to prior enzymatic and mechanical dissociation. The facility and simplicity of the whole fetal pancreas implantation technique makes it an appealing model for further study of islet growth and differentiation at the transplant site and of its effect on the metabolic state of the recipient.