Long-term resveratrol administration improves diabetes-induced pancreatic oxidative stress, inflammatory status, and ß cell function in male rats

Abstract Diabetes is a metabolic disorder caused by insulin resistance or a defect in the pancreatic beta cells in insulin secretion. The aim of this study was to evaluate the possible effectiveness of long-term administration of resveratrol on inflammatory and oxidative stress markers in the pancreatic tissue of diabetic rats. Male Wistar rats (n = 24) were randomly divided into four groups of six animals, namely a healthy group, a healthy group receiving resveratrol, a diabetic control group, and a diabetic group receiving resveratrol. Diabetes was induced by single dose injection of streptozotocin (50 mg/kg; ip), 15 min after injection of nicotinamide (110 mg/kg; ip). Resveratrol was also administered by gavage (5 mg/kg/day) for 4 months. Administration of resveratrol alleviated hyperglycemia, weight loss and pancreatic ß cell function measured by HOMA-ß. Resveratrol improved oxidative stress (nitrate/nitrite, 8-isoprostane and glutathione) and proinflammatory markers (tumor necrosis factor α, cyclooxygenase 2, interleukin 6 and nuclear factor kappa B) in the pancreatic tissue of diabetic rats. Resveratrol administration had no significant effect on the activity of superoxide dismutase and catalase enzyme. These observations indicate that resveratrol administration may be effective as a beneficial factor in improving pancreatic function and reducing the complications of diabetes

Pancreatic Ppy-expressing γ-cells display mixed phenotypic traits and the adaptive plasticity to engage insulin production.

The cellular identity of pancreatic polypeptide (Ppy)-expressing γ-cells, one of the rarest pancreatic islet cell-type, remains elusive. Within islets, glucagon and somatostatin, released respectively from α- and δ-cells, modulate the secretion of insulin by ß-cells. Dysregulation of insulin production raises blood glucose levels, leading to diabetes onset. Here, we present the genetic signature of human and mouse γ-cells. Using different approaches, we identified a set of genes and pathways defining their functional identity. We found that the γ-cell population is heterogeneous, with subsets of cells producing another hormone in addition to Ppy. These bihormonal cells share identity markers typical of the other islet cell-types. In mice, Ppy gene inactivation or conditional γ-cell ablation did not alter glycemia nor body weight. Interestingly, upon ß-cell injury induction, γ-cells exhibited gene expression changes and some of them engaged insulin production, like α- and δ-cells. In conclusion, we provide a comprehensive characterization of γ-cells and highlight their plasticity and therapeutic potential.

Pancreatic ß-cell heterogeneity in health and diabetes: classes, sources, and subtypes.

Pancreatic ß-cells perform glucose-stimulated insulin secretion, a process at the center of type 2 diabetes etiology. Efforts to understand how ß-cells behave in healthy and stressful conditions have revealed a wide degree of morphological, functional, and transcriptional heterogeneity. Sources of heterogeneity include ß-cell topography, developmental origin, maturation state, and stress response. Advances in sequencing and imaging technologies have led to the identification of ß-cell subtypes, which play distinct roles in the islet niche. This review examines ß-cell heterogeneity from morphological, functional, and transcriptional perspectives, and considers the relevance of topography, maturation, development, and stress response. It also discusses how these factors have been used to identify ß-cell subtypes, and how heterogeneity is impacted by diabetes. We examine open questions in the field and discuss recent technological innovations that could advance understanding of ß-cell heterogeneity in health and disease.

Oral delivery of exenatide-loaded hybrid zein nanoparticles for stable blood glucose control and ß-cell repair of type 2 diabetes mice.

BACKGROUND: Exenatide is an insulinotropic peptide drug for type 2 diabetes treatment with low risk of hypoglycemia, and is administrated by subcutaneous injection. Oral administration is the most preferred route for lifelong treatment of diabetes, but oral delivery of peptide drug remains a significant challenge due to the absorption obstacles in gastrointestinal tract. We aimed to produce exenatide-loaded nanoparticles containing absorption enhancer, protectant and stabilizer using FDA approved inactive ingredients and easy to scale-up method, and to evaluate their long-term oral therapeutic effect in type 2 diabetes db/db mice. RESULTS: Two types of nanoparticles, named COM NPs and DIS NPs, were fabricated using anti-solvent precipitation method. In COM NPs, the exenatide was complexed with cholic acid and phosphatidylcholine to increase the exenatide loading efficiency. In both nanoparticles, zein acted as the cement and the other ingredients were embedded in zein nanoparticles by hydrophobic interaction. Casein acted as the stabilizer. The nanoparticles had excellent lyophilization, storage and re-dispersion stability. Hypromellose phthalate protected the loaded exenatide from degradation in simulated gastric fluid. Cholic acid promoted the intestinal absorption of the loaded exenatide via bile acid transporters. The exenatide loading efficiencies of COM NPs and DIS NPs were 79.7% and 53.6%, respectively. The exenatide oral pharmacological availability of COM NPs was 18.6% and DIS NPs was 13.1%. COM NPs controlled the blood glucose level of the db/db mice well and the HbA1c concentration significantly decreased to 6.8% during and after 7 weeks of once daily oral administration consecutively. Both DIS NPs and COM NPs oral groups substantially increased the insulin secretion by more than 60% and promoted the ß-cell proliferation by more than 120% after the 7-week administration. CONCLUSIONS: Both COM NPs and DIS NPs are promising systems for oral delivery of exenatide, and COM NPs are better in blood glucose level control than DIS NPs. Using prolamin to produce multifunctional nanoparticles for oral delivery of peptide drug by hydrophobic interaction is a simple and effective strategy.

Charting cellular identity during human in vitro ß-cell differentiation.

In vitro differentiation of human stem cells can produce pancreatic ß-cells; the loss of this insulin-secreting cell type underlies type 1 diabetes. Here, as a step towards understanding this differentiation process, we report the transcriptional profiling of more than 100,000 human cells undergoing in vitro ß-cell differentiation, and describe the cells that emerged. We resolve populations that correspond to ß-cells, α-like poly-hormonal cells, non-endocrine cells that resemble pancreatic exocrine cells and a previously unreported population that resembles enterochromaffin cells. We show that endocrine cells maintain their identity in culture in the absence of exogenous growth factors, and that changes in gene expression associated with in vivo ß-cell maturation are recapitulated in vitro. We implement a scalable re-aggregation technique to deplete non-endocrine cells and identify CD49a (also known as ITGA1) as a surface marker of the ß-cell population, which allows magnetic sorting to a purity of 80%. Finally, we use a high-resolution sequencing time course to characterize gene-expression dynamics during the induction of human pancreatic endocrine cells, from which we develop a lineage model of in vitro ß-cell differentiation. This study provides a perspective on human stem-cell differentiation, and will guide future endeavours that focus on the differentiation of pancreatic islet cells, and their applications in regenerative medicine.

Machine learning based classification of cells into chronological stages using single-cell transcriptomics.

Age-associated deterioration of cellular physiology leads to pathological conditions. The ability to detect premature aging could provide a window for preventive therapies against age-related diseases. However, the techniques for determining cellular age are limited, as they rely on a limited set of histological markers and lack predictive power. Here, we implement GERAS (GEnetic Reference for Age of Single-cell), a machine learning based framework capable of assigning individual cells to chronological stages based on their transcriptomes. GERAS displays greater than 90% accuracy in classifying the chronological stage of zebrafish and human pancreatic cells. The framework demonstrates robustness against biological and technical noise, as evaluated by its performance on independent samplings of single-cells. Additionally, GERAS determines the impact of differences in calorie intake and BMI on the aging of zebrafish and human pancreatic cells, respectively. We further harness the classification ability of GERAS to identify molecular factors that are potentially associated with the aging of beta-cells. We show that one of these factors, junba, is necessary to maintain the proliferative state of juvenile beta-cells. Our results showcase the applicability of a machine learning framework to classify the chronological stage of heterogeneous cell populations, while enabling detection of candidate genes associated with aging.

Evidence for a Neogenic Niche at the Periphery of Pancreatic Islets.

We recently discovered a novel subset of beta cells that resemble immature beta cells during pancreas development. We named these "virgin" beta cells as they do not stem from existing mature beta cells. Virgin beta cells are found exclusively at the islet periphery in areas that we therefore designated as the "neogenic niche." As beta cells are our only source of insulin, their loss leads to diabetes. Islets also contain glucagon-producing alpha cells and somatostatin-producing delta cells, that are important for glucose homeostasis and form a mantle surrounding the beta cell core. This 3D architecture is important and determines access to blood flow and innervation. We propose that the distinctive islet architecture may also play an important, but hitherto unappreciated role in generation of new endocrine cells, including beta cells. We discuss several predictions to further test the contribution of the neogenic niche to beta cell regeneration.

Mecanismos moleculares mediadores da citoproteção de células beta pancreáticas induzidos por prolactina / Role of HSPB1 in PRL-induced cytoprotective effects on beta cells

A manutenção da célula de ilhotas in vitro aparece como uma estratégia atraente para aumentar o resultado do transplante de ilhotas pancreáticas. Entretanto, o destino das ilhotas em cultura é determinado pelo equilíbrio entre mediadores pró e antiapoptóticos. Nós mostramos anteriormente que os níveis de HSPB1 são aumentados pela prolactina (PRL) tanto nas células beta pancreáticas humanas quanto nas células de insulinoma murino MIN6. Além disso, mostramos que os efeitos pró- sobrevivência induzidos pela prolactina nas células beta pancreáticas são mediados pela HSPB1. Uma vez que o papel da HSPB1 nas células beta não foi estudado diretamente, procuramos explorar os mecanismos moleculares pelos quais a HSPB1 medeia a citoproteção da célula beta induzida pela PRL. Para isso, células MIN6 derivadas de um insulinoma de camundongo e cultura primária de ilhotas pancreáticas murinas (I), silenciadas ou superexpressando HSPB1 foram submetidas à privação de soro e então pré- tratadas na presença ou na ausência de PRL (300 ng / mL) e expostos a ou citocinas (IL-1ß (0,8 ng / mL), IFN-γ (4 ng / mL) e TNF-α (8 ng / mL) por 16 ou 24 h. Após esses períodos de tempo foi avaliada a viabilidade celular. De fato, as células silenciadas para HSPB1 tiveram maiores porcentagens de morte celular em comparação aos controles. No entanto, a superexpressão de HSPB1 sozinha imita os efeitos citoprotectores da Prolactina em ambas as células MIN6 e nas culturas primárias das ilhotas. Estes resultados mostram o papel fundamental da HSPB1 no efeito citoprotetor inibindo a apoptose inducida pelo tratamento com citocinas pró-inflamatórias. Além disso, os lisados de células Min6 tratadas com citocinas na presença ou na ausência de PRL durante 6 h foram sujeitos a imunoprecipitação de HSPB1. Proteínas coimmunoprecipitadas separadaspor SDS-PAGE e posteriormente identificadas por nano-HPLC acoplado à espectrometria de massas. Células pré-tratadas com PRL apresentaram um enriquecimento de proteínas que coprescipitaram com HSPB1 relacionadas em processos de resistência ao estresse oxidativo, degradação proteica e metabolismo de carboidratos. Células MIN6, silenciadas ou superexpressando HSPB1 foram expostas á menadiona e peróxido de hidrogênio e parâmetros oxidativos foram analisados. O silenciamento de HSPB1 promoveu células mais sensíveis ao estresse oxidativo e levou a uma redução da capacidade antioxidante, enquanto que prolactina induziu citoproteção mediada por HSPB1 contra o estresse oxidativo. A superexpressão de HSPB1, no entanto, levou a efeitos opostos. O tratamento com PRL, o silenciamento ou superexpressão de HSPB1 não mudou a expressão de enzimas antioxidantes, mas os níveis proteicos de HSPB1 estão relacionados com a modulação da razão GSH/GSSG e a atividade de G6PD. Dado de estudos recentes reportam que o perfil respiratório das ilhotas prévias ao transplante pode predizer seu desempenho e que não se sabe nada sobre se a PRL poderia modular a função mitocondrial nas células beta; no presente projeto foi investigado se o tratamento hormonal poderia aumentar a eficiência mitocondrial das células beta. Observamos que o tratamento com citocinas pró-inflamatórias produziu uma diminuição na eficiência do consumo de oxigênio mitocondrial estar relacionado à síntese de ATP. Esses resultados foram significativamente revertidos a valores similares ao obtidos nas células submetidas Às condições de máxima viabilidade após o tratamento com PRL. Além disso, os resultados mostraram que os níveis elevados de HSPB1 medeiam este efeito, uma vez que a falta desta proteína anulou significativamente a recuperação da função mitocondrial induzida pelo tratamento hormonal. Visto que as taxas de síntese de ATP mitocondrial são as responsáveis pela elevação na sua concentração intracelular e que esse evento está diretamente relacionado com a secreção de insulina nas células beta, analisamos se diferentes níveis proteicos de HSPB1 poderia modificar a função secretora de células beta. Para isso foram calculados os índices de estímulo da secreção de insulina em resposta ao aumento da concentraçãode glicose no meio de cultura tanto em células parentais MIN6 como em culturas primárias de ilhotas pancreáticas murinas que foram submetidas ou não ao silenciamento ou superexpressão de HSPB1. Nossos resultados mostraram que nem a presença de citocinas, Prolactina, ou a ausência ou superexpressão de HSPB1 nas culturas celulares analisadas apresentaram diferença significativa em relação aos índices de estímulo da secreção e conteúdo de insulina. Esses resultados sugerem que nem a falta, nem a superexpressão de HSPB1 poderia alterar a função de célula beta. Nós mostramos a relevância da HSPB1 em ambos os efeitos pró- sobrevivência da PRL contra a morte da célula beta induzida tanto por citocinas quanto por indução de estresse oxidativo. Este último efeito poderia também estar relacionado com a participação da HSPB1 na recuperação da função mitocondrial observada após o tratamento hormonal corroborando assim parte dos resultados obtidos nos experimentos de immunoprecipitação. Finalmente, nossos resultados destacam a importância de mais estudos visando um entendimento mais profundo das funções da HSPB1 nas células beta, uma vez que elas poderiam levar à mitigação da morte da célula beta através da regulação positiva de uma via de proteção endógena, que não é dependente da modulação do sistema imunológico

The success of islet transplantation has improved lately. Unfortunately, it is still compromised by cell loss. Maintaining islet cell in vitro appears as an attractive strategy to increase the outcome of pancreatic islet transplantation. However, islet fate in culture is determined by the balance between pro- and anti- apoptotic mediators. We have previously shown that Heat Shock Protein B1 (HSPB1) levels are increased by prolactin (PRL) on both human pancreatic beta cells and MIN6 murine insulinoma cells. Furthermore, we have demonstrated the prolactin-induced pro-survival effects on pancreatic beta-cells are mediated by HSPB1. Since HSPB1 role in beta cells has not been directly studied, we set out to explore the molecular mechanisms by which HSPB1 mediates PRL-induced beta cell cytoprotection. For this purpose, MIN6 insulinoma mouse cells and primary culture of murine pancreatic islets (I) wild type, HSPB1 silenced or overexpressing the chaperone were subjected to serum starvation and then pre-treated in the presence or in the absence of PRL (300 ng/mL) and exposed to or cytokines (IL-1ß (0,8 ng/mL), IFN-γ (4 ng/mL) and TNF-α (8 ng/mL)) for 16 or 24h. Then, we analyse cell viability. HSPB1silenced cells presented higher percentages of cell death compared to controls. However, the overexpression of HSPB1, independently of hormonal treatment, was able mimic the cytoprotective effects of Prolactin. These results point at the key role of HSPB1 in the cytoprotective effect against proinflammatory cytokines-induced beta cell death. In addition, lysates from Min6 cells incubated for 6 hours in the presence of a cocktail of cytokines and/or PRL were subjected to HSPB1 immunoprecipitation. Co-precipitated proteins were identified by SDS-PAGE coupled to mass spectrometry. We found an enrichment of proteins relatedto signaling pathways involved in a response against oxidative and endoplasmic reticulum stress induction. Moreover, we also identified antiapoptotic effects and carbohydrate metabolism related proteins. Indeed, HSPB1 knockdown rendered cells more sensitive to oxidative stress and led to a reduced antioxidant capacity, while prolactin induced an HSPB1- mediated cytoprotection against ROS induced beta-cell apoptosis. One again, HSPB1 overexpression mimic PRL- induced cytoprotection. While hormonal treatment, HSPB1 silencing or overexpression did not change the expression of antioxidant enzymes; this conditions influenced reduced glutathione cell content and G6DP activity. Since recent studies have pointed that islets respiratory profile prior to transplantation may predict their performance; we also investigated whether PRL treatment could increase beta-cell mitochondrial efficiency. We observed a cytokine-induced increase of mitochondrial oxygen consumption rate not related to ATP synthesis, which was significantly decreased upon PRL treatment. HSPB1 was a key mediator of this effect since the lack of this protein significantly abrogated PRL-induced mitochondrial function recovery. The secretory function was then analysed in wild type MIN6 cells as well as in primary cultures of pancreatic islets either HSPB1 silenced or overexpressing the chaperone. Cells were subjected to serum starvation and then pre-treated in the presence or in the absence of PRL and exposed to cytokines for 16 or 24h. We didn´t found significant differences in both glucose induced-insulin secretion and insulin content between the hormonal treatment, HSPB1 silencing or overexpression. These results suggest that neither lack, nor overexpression of HSPB1 could alter beta cell function. Altogether our results have shown the importance of HSPB1 on PRL prosurvival effects as well as on maintenance of mitochondrial efficiency against both cytokine treatment and oxidative-stress-induced beta cell damage. These results are in accordance with the PRL-induced enrichment of HSPB1 interacting proteins displaying functions related to protein degradation, oxidative stress protection or mitochondrial carbohydrate metabolism.Finally, our results outline the importance of further studies aiming at a deeper understanding of HSPB1 functions on beta cells, since they could lead to the mitigation of beta cell death through the up-regulation of an endogenous protective pathway, which is not dependent on the modulation of the immune system

Single-cell transcriptomes reveal characteristic features of human pancreatic islet cell types.

Pancreatic islets of Langerhans contain several specialized endocrine cell types, which are commonly identified by the expression of single marker genes. However, the established marker genes cannot capture the complete spectrum of cellular heterogeneity in human pancreatic islets, and existing bulk transcriptome datasets provide averages across several cell populations. To dissect the cellular composition of the human pancreatic islet and to establish transcriptomes for all major cell types, we performed single-cell RNA sequencing on 70 cells sorted from human primary tissue. We used this dataset to validate previously described marker genes at the single-cell level and to identify specifically expressed transcription factors for all islet cell subtypes. All data are available for browsing and download, thus establishing a useful resource of single-cell expression profiles for endocrine cells in human pancreatic islets.

PAX4 Defines an Expandable ß-Cell Subpopulation in the Adult Pancreatic Islet.

PAX4 is a key regulator of pancreatic islet development whilst in adult acute overexpression protects ß-cells against stress-induced apoptosis and stimulates proliferation. Nonetheless, sustained PAX4 expression promotes ß-cell dedifferentiation and hyperglycemia, mimicking ß-cell failure in diabetic patients. Herein, we study mechanisms that allow stringent PAX4 regulation endowing favorable ß-cell adaptation in response to changing environment without loss of identity. To this end, PAX4 expression was monitored using a mouse bearing the enhanced green fluorescent protein (GFP) and cre recombinase construct under the control of the islet specific pax4 promoter. GFP was detected in 30% of islet cells predominantly composed of PAX4-enriched ß-cells that responded to glucose-induced insulin secretion. Lineage tracing demonstrated that all islet cells were derived from PAX4(+) progenitor cells but that GFP expression was confined to a subpopulation at birth which declined with age correlating with reduced replication. However, this GFP(+) subpopulation expanded during pregnancy, a state of active ß-cell replication. Accordingly, enhanced proliferation was exclusively detected in GFP(+) cells consistent with cell cycle genes being stimulated in PAX4-overexpressing islets. Under stress conditions, GFP(+) cells were more resistant to apoptosis than their GFP(-) counterparts. Our data suggest PAX4 defines an expandable ß-cell sub population within adult islets.

Pancreatic beta cell protection/regeneration with phytotherapy

Although currently available drugs are useful in controlling early onset complications of diabetes, serious late onset complications appear in a large number of patients. Considering the physiopathology of diabetes, preventing beta cell degeneration and stimulating the endogenous regeneration of islets will be essential approaches for the treatment of insulin-dependent diabetes mellitus. The current review focused on phytochemicals, the antidiabetic effect of which has been proved by pancreatic beta cell protection/regeneration. Among the hundreds of plants that have been investigated for diabetes, a small fraction has shown the regenerative property and was described in this paper. Processes of pancreatic beta cell degeneration and regeneration were described. Also, the proposed mechanisms for the protective/regenerative effects of such phytochemicals and their potential side effects were discussed.

Embora medicamentos disponíveis atualmente sejam úteis no controle de complicações da Diabetes, complicações aparecem em grande número de pacientes. Considerando-se a fisiopatologia do Diabetes, a prevenção da degeneração de células beta e o estímulo da regeneração endógena de ilhotas será abordagem essencial para o tratamento de diabetes mellitus insulino-dependente. A presente revisão aborda compostos fitoquímicos, cujo efeito é provado na proteção/regeneração de células beta de pâncreas. Entre centenas de plantas que têm sido investigadas para o diabetes, pequena fração tem mostrado propriedade regenerativa, que será descrita neste trabalho. Os processos de degeneração e de regeneração das células beta do pâncrease são descritos. Além disso, mecanismos propostos para efeitos de proteção e regeneração desses compostos fitoquímicos e seus possíveis efeitos colaterais também serão discutidos neste trabalho.

Placental lactogens induce serotonin biosynthesis in a subset of mouse beta cells during pregnancy.

AIMS/HYPOTHESIS: Upregulation of the functional beta cell mass is required to match the physiological demands of mother and fetus during pregnancy. This increase is dependent on placental lactogens (PLs) and prolactin receptors, but the mechanisms underlying these events are only partially understood. We studied the mRNA expression profile of mouse islets during pregnancy to gain a better insight into these changes. METHODS: RNA expression was measured ex vivo via microarrays and quantitative RT-PCR. In vivo observations were extended by in vitro models in which ovine PL was added to cultured mouse islets and MIN6 cells. RESULTS: mRNA encoding both isoforms of the rate-limiting enzyme of serotonin biosynthesis, tryptophan hydroxylase (TPH), i.e. Tph1 and Tph2, were strongly induced (fold change 25- to 200-fold) during pregnancy. This induction was mimicked by exposing islets or MIN6 cells to ovine PLs for 24 h and was dependent on janus kinase 2 and signal transducer and activator of transcription 5. Parallel to Tph1 mRNA and protein induction, islet serotonin content increased to a peak level that was 200-fold higher than basal. Interestingly, only a subpopulation of the beta cells was serotonin-positive in vitro and in vivo. The stored serotonin pool in pregnant islets and PL-treated MIN6 cells was rapidly released (turnover once every 2 h). CONCLUSIONS/INTERPRETATION: A very strong lactogen-dependent upregulation of serotonin biosynthesis occurs in a subpopulation of mouse islet beta cells during pregnancy. Since the newly formed serotonin is rapidly released, this lactogen-induced beta cell function may serve local or endocrine tasks, the nature of which remains to be identified.

Characterization of pancreatic ductal cells in human islet preparations.

Substantial amounts of nonendocrine cells are implanted as part of human islet grafts, and a possible influence of nonendocrine cells on clinical islet transplantation outcome has been postulated. There are currently no product release criteria specific for nonendocrine cells due to lack of available methods. The aims of this study were to develop a method for the evaluation of pancreatic ductal cells (PDCs) for clinical islet transplantation and to characterize them regarding phenotype, viability, and function. We assessed 161 human islet preparations using laser scanning cytometry (LSC/iCys) for phenotypic analysis of nonendocrine cells and flow cytometry (FACS) for PDC viability. PDC and beta-cells obtained from different density fractions during the islet cell purification were compared in terms of viability. Furthermore, we examined PDC ability to produce proinflammatory cytokines/chemokines, vascular endothelial growth factor (VEGF) and tissue factor (TF) relevant to islet graft outcome. Phenotypic analysis by LSC/iCys indicated that single staining for CK19 or CA19-9 was not enough for identifying PDCs, and that double staining for amylase and CK19 or CA19-9 allowed for quantitative evaluation of acinar cells and PDC content in human islet preparation. PDC showed a significantly higher viability than beta-cells (PDC vs beta-cell: 75.5+/-13.9 and 62.7+/-18.7%; P<0.0001). Although beta-cell viability was independent of its density, that of PDCs was higher as the density from which they were recovered increased. There was no correlation between PDCs and beta-cell viability (R(2)=0.0078). PDCs sorted from high-density fractions produced significantly higher amounts of proinflammatory mediators and VEGF, but not TF. We conclude that PDCs isolated from different fractions had different viability and functions. The precise characterization and assessment of these cells in addition to beta-cells in human islet cell products may be of assistance in understanding their contribution to islet engraftment and in developing strategies to enhance islet graft function.