Insulin release and suppression by tacrolimus, rapamycin and cyclosporin A are through regulation of the ATP-sensitive potassium channel

Pancreatic β-cell mitophagy as an adaptive response to metabolic stress and the underlying mechanism that involves lysosomal Ca2+ release

Mitophagy is an excellent example of selective autophagy that eliminates damaged or dysfunctional mitochondria, and it is crucial for the maintenance of mitochondrial integrity and function. The critical roles of autophagy in pancreatic β-cell structure and function have been clearly shown. Furthermore, morphological abnormalities and decreased function of mitochondria have been observed in autophagy-deficient β-cells, suggesting the importance of β-cell mitophagy. However, the role of authentic mitophagy in β-cell function has not been clearly demonstrated, as mice with pancreatic β-cell-specific disruption of Parkin, one of the most important players in mitophagy, did not exhibit apparent abnormalities in β-cell function or glucose homeostasis. Instead, the role of mitophagy in pancreatic β-cells has been investigated using β-cell-specific Tfeb-knockout mice (TfebΔβ-cell mice); Tfeb is a master regulator of lysosomal biogenesis or autophagy gene expression and participates in mitophagy. TfebΔβ-cell mice were unable to adaptively increase mitophagy or mitochondrial complex activity in response to high-fat diet (HFD)-induced metabolic stress. Consequently, TfebΔβ-cell mice exhibited impaired β-cell responses and further exacerbated metabolic deterioration after HFD feeding. TFEB was activated by mitochondrial or metabolic stress-induced lysosomal Ca2+ release, which led to calcineurin activation and mitophagy. After lysosomal Ca2+ release, depleted lysosomal Ca2+ stores were replenished by ER Ca2+ through ER→lysosomal Ca2+ refilling, which supplemented the low lysosomal Ca2+ capacity. The importance of mitophagy in β-cell function was also demonstrated in mice that developed β-cell dysfunction and glucose intolerance after treatment with a calcineurin inhibitor that hampered TFEB activation and mitophagy.

Impaired TFEB activation and mitophagy as a cause of PPP3/calcineurin inhibitor-induced pancreatic β-cell dysfunction

Macroautophagy/autophagy or mitophagy plays crucial roles in the maintenance of pancreatic β-cell function. PPP3/calcineurin can modulate the activity of TFEB, a master regulator of lysosomal biogenesis and autophagy gene expression, through dephosphorylation. We studied whether PPP3/calcineurin inhibitors can affect the mitophagy of pancreatic β-cells and pancreatic β-cell function employing FK506, an immunosuppressive drug against graft rejection. FK506 suppressed rotenone- or oligomycin+antimycin-A-induced mitophagy measured by Mito-Keima localization in acidic lysosomes or RFP-LC3 puncta colocalized with TOMM20 in INS-1 insulinoma cells. FK506 diminished nuclear translocation of TFEB after treatment with rotenone or oligomycin+antimycin A. Forced TFEB nuclear translocation by a constitutively active TFEB mutant transfection restored impaired mitophagy by FK506, suggesting the role of decreased TFEB nuclear translocation in FK506-mediated mitophagy impairment. Probably due to reduced mitophagy, recovery of mitochondrial potential or quenching of mitochondrial ROS after removal of rotenone or oligomycin+antimycin A was delayed by FK506. Mitochondrial oxygen consumption was reduced by FK506, indicating reduced mitochondrial function by FK506. Likely due to mitochondrial dysfunction, insulin release from INS-1 cells was reduced by FK506 in vitro. FK506 treatment also reduced insulin release and impaired glucose tolerance in vivo, which was associated with decreased mitophagy and mitochondrial COX activity in pancreatic islets. FK506-induced mitochondrial dysfunction and glucose intolerance were ameliorated by an autophagy enhancer activating TFEB. These results suggest that diminished mitophagy and consequent mitochondrial dysfunction of pancreatic β-cells contribute to FK506-induced β-cell dysfunction or glucose intolerance, and autophagy enhancement could be a therapeutic modality against post-transplantation diabetes mellitus caused by PPP3/calcineurin inhibitors.

pre-existing diabetes and PTDM in kidney transplant recipients: how to handle immunosuppression

INTRODUCTION

Preexisting diabetes (PD) and post-transplant diabetes mellitus (PTDM) are common and severe comorbidities posttransplantation. The immunosuppressive regimens are modifiable risk factors.

AREAS COVERED

We reviewed Pubmed and Cochrane database and we summarize the mechanisms and impacts of available immunosuppressive treatments on the risk of PD and PTDM. We also assess the possible management of these drugs to improve glycemic parameters while considering risks inherent in transplantation.

EXPERT OPINION

PD i) increases the risk of sepsis, ii) is an independent risk factor for infection-related mortality, and iii) increases acute rejection risk. Regarding PTDM development i) immunosuppressive strategies without corticosteroids significantly reduce the risk but the price may be a higher incidence of rejection; ii) minimization or rapid withdrawal of steroids are two valuable approaches; iii) the diabetogenic role of calcineurin inhibitors(CNIs) is also well-described and is more important for tacrolimus than for cyclosporine. Reducing tacrolimus-exposure may improve glycemic parameters but also has a higher risk of rejection. PTDM risk is higher in patients that receive sirolimus compared to mycophenolate mofetil. Finally, conversion from CNIs to belatacept may offer the best benefits to PTDM-recipients in terms of glycemic parameters, graft and patient-outcomes.

Targeted Systemic Treatment of Neuroendocrine Tumors: Current Options and Future Perspectives

Neuroendocrine tumors (NETs) originate from the neuroendocrine cell system in the bronchial and gastrointestinal tract and can produce hormones leading to distinct clinical syndromes. Systemic treatment of patients with unresectable NETs aims to control symptoms related to hormonal overproduction and tumor growth. In the last decades prognosis has improved as a result of increased detection of early stage disease and the introduction of somatostatin analogs (SSAs) as well as several new therapeutic options. SSAs are the first-line medical treatment of NETs and can control hormonal production and tumor growth. The development of next-generation multireceptor targeted and radiolabelled somatostatin analogs, as well as target-directed therapies (as second-line treatment options) further improve progression-free survival in NET patients. To date, however, a significant prolongation of overall survival with systemic treatment in NET has not been convincingly demonstrated. Several new medical options and treatment combinations will become available in the upcoming years, and although preliminary results of preclinical and clinical trials are encouraging, large, preferrably randomized clinical studies are required to provide definitive evidence of their effect on survival and symptom control.

Multidisciplinary management of refractory insulinomas

Insulinomas are predominantly benign (~90%), pancreatic neuroendocrine tumours characterized by hyperinsulinaemic hypoglycaemia. They usually present as a small (<2 cm), well-demarcated, solitary nodule that can arise in any part of the organ. Treatment for sporadic insulinomas is generally aimed at curative surgical resection with special consideration in genetic syndromes. Patients with significant hypoglycaemia can pose a difficult management challenge. In isolated cases where the patient is not medically fit for surgery or with metastatic spread, other treatment options are employed. Medical therapy with diazoxide or somatostatin analogues is commonly used first line for symptom control, albeit with variable efficacy. Other medical options are emerging, including newer targeted biological therapies, including everolimus (an mTOR inhibitor), sunitinib (a tyrosine kinase inhibitor) and pasireotide, a multisomatostatin receptor ligand. Pasireotide and everolimus both cause hyperglycaemia by physiological mechanisms synergistic with its antitumour/antiproliferative effects. Minimally invasive treatment modalities such as ethanol ablation are available in selected cases (particularly in patients unfit for surgery), peptide receptor radionuclide therapy (PRRT) can effectively control tumour growth or provide symptomatic benefit in metastatic disease, while cytotoxic chemotherapy can be used in patients with higher-grade tumours. This review considers the developments in the medical and other nonsurgical management options for cases refractory to standard medical management. Early referral to a dedicated neuroendocrine multidisciplinary team is critical considering the array of medical, oncological, interventional radiological and nuclear medical options. We discuss the evolving armamentarium for insulinomas when standard medical therapy fails.

Post-Liver Transplantation Diabetes Mellitus: A Review of Relevance and Approach to Treatment

Post-liver transplantation diabetes mellitus (PLTDM) develops in up to 30% of liver transplant recipients and is associated with increased risk of mortality and multiple morbid outcomes. PLTDM is a multicausal disorder, but the main risk factor is the use of immunosuppressive agents of the calcineurin inhibitor (CNI) family (tacrolimus and cyclosporine). Additional factors, such as pre-transplant overweight, nonalcoholic steatohepatitis and hepatitis C virus infection, may further increase risk of developing PLTDM. A diagnosis of PLTDM should be established only after doses of CNI and steroids are stable and the post-operative stress has been overcome. The predominant defect induced by CNI is insulin secretory dysfunction. Plasma glucose control must start immediately after the transplant procedure in order to improve long-term results for both patient and transplant. Among the better known antidiabetics, metformin and DPP-4 inhibitors have a particularly benign profile in the PLTDM context and are the preferred oral agents for long-term management. Insulin therapy is also an effective approach that addresses the prevailing pathophysiological defect of the disorder. There is still insufficient evidence about the impact of newer families of antidiabetics (GLP-1 agonists, SGLT-2 inhibitors) on PLTDM. In this review, we summarize current knowledge on the epidemiology, pathogenesis, course of disease and medical management of PLTDM.

Sirolimus induces depletion of intracellular calcium stores and mitochondrial dysfunction in pancreatic beta cells

Sirolimus (rapamycin) is an immunosuppressive drug used in transplantation. One of its major side effects is the increased risk of diabetes mellitus; however, the exact mechanisms underlying such association have not been elucidated. Here we show that sirolimus impairs glucose-stimulated insulin secretion both in human and murine pancreatic islets and in clonal β cells in a dose- and time-dependent manner. Importantly, we demonstrate that sirolimus markedly depletes calcium (Ca²⁺) content in the endoplasmic reticulum and significantly decreases glucose-stimulated mitochondrial Ca²⁺ uptake. Crucially, the reduced mitochondrial Ca²⁺ uptake is mirrored by a significant impairment in mitochondrial respiration. Taken together, our findings indicate that sirolimus causes depletion of intracellular Ca²⁺ stores and alters mitochondrial fitness, eventually leading to decreased insulin release. Our results provide a novel molecular mechanism underlying the increased incidence of diabetes mellitus in patients treated with this drug.

Risk of hyperglycemia attributable to everolimus in cancer patients: A meta-analysis

Everolimus has been used widely in cancer patients and is associated with the development of hyperglycemia. Due to confounding factors, its specific impact on hyperglycemia has not been well understood. We performed a meta-analysis of randomized controlled trials to determine the risk of hyperglycemia attributable to everolimus in cancer patients of varying tumor types.

MATERIAL AND METHODS

PubMed and American Society of Clinical Oncology conference abstracts up to June 2015 were systematically searched. Eligible studies included randomized controlled trials (RCTs) in which everolimus was compared to placebo in cancer patients with or without other agents. Heterogeneity tests were performed to examine between-study differences in hyperglycemia, and the incidence and relative risk of all- and high-grade hyperglycemia attributable to everolimus were determined using both random- or fixed-effects models.

RESULTS

A total of seven phase III and two phase II RCTs with various tumors, encompassing a total of 3879 cancer patients, were included in our analysis. Everolimus significantly increased the risk of all-grade (RR =2.60, 95% CI 2.03-3.31, p < 0.001) and high-grade (RR =3.0, 95% CI 1.72-5.23; p < 0.001) hyperglycemia. The incidences of all- and high-grade hyperglycemia attributable to everolimus were 6.8% (95% CI 3.4-13.2%) and 2.5% (95% CI 1.2-4.9%), respectively. The everolimus-specific risk of all-grade hyperglycemia varied significantly with tumor types (p < 0.001), with the highest incidence seen in renal cell carcinoma (RCC) (27.2%, 95% CI 22.2-32.8%) and the lowest in breast cancer (3.3%, 95% CI 1.3-8.2%). No significant variation was found between everolimus alone or everolimus in combination with other agents. Similar results were also found for the risk of high-grade hyperglycemia attributable to everolimus.

CONCLUSION

The specific risk of hyperglycemia attributable to everolimus may vary significantly with tumor types. Close monitoring should be given to patients at high risk, such as RCC.

Acute rapamycin treatment improved glucose tolerance through inhibition of hepatic gluconeogenesis in rainbow trout (Oncorhynchus mykiss)

Our aim was to investigate the potential role of TOR (target of rapamycin) signaling pathway in the regulation of hepatic glucose metabolism in rainbow trout. Fasted fish were first treated with a single intraperitoneal injection of rapamycin or vehicle and then submitted to a second intraperitoneal administration of glucose 4 h later. Our results revealed that intraperitoneal administration of glucose induced hyperglycemia for both vehicle and rapamycin treatments, which peaked at 2 h. Plasma glucose level in vehicle-treated fish was significantly higher than in rapamycin-treated fish at 8 and 17 h, whereas it remained at the basal level in rapamycin-treated fish. Glucose administration significantly enhanced the phosphorylation of Akt and ribosomal protein S6 kinase (S6K1) in vehicle-treated fish, while rapamycin completely abolished the activation of S6K1 in rapamycin-treated fish, without inhibiting the phosphorylation of Akt on Thr-308 or Ser-473. Despite the lack of significant variation in phosphoenolpyruvate carboxykinase mRNA abundance, mRNA abundance for glucokinase (GK), glucose 6-phosphatase (G6Pase) I and II, and fructose 1,6-bisphosphatase (FBPase) was reduced by rapamycin 17 h after glucose administration. The inhibition effect of rapamycin on GK and FBPase was further substantiated at the activity level. The suppression of GK gene expression and activity by rapamycin provided the first in vivo evidence in fish that glucose regulates hepatic GK gene expression and activity through a TORC1-dependent manner. Unlike in mammals, we observed that acute rapamycin treatment improved glucose tolerance through the inhibition of hepatic gluconeogenesis in rainbow trout.

Diabetes mellitus in the transplanted kidney

Diabetes mellitus (DM) is the most common cause of chronic kidney disease and end stage renal disease. New onset diabetes mellitus after transplant (NODAT) has been described in approximately 30% of non-diabetic kidney-transplant recipients many years post transplantation. DM in patients with kidney transplantation constitutes a major comorbidity, and has significant impact on the patients and allografts' outcome. In addition to the major comorbidity and mortality that result from cardiovascular and other DM complications, long standing DM after kidney-transplant has significant pathological injury to the allograft, which results in lowering the allografts and the patients' survivals. In spite of the cumulative body of data on diabetic nephropathy (DN) in the native kidney, there has been very limited data on the DN in the transplanted kidney. In this review, we will shed the light on the risk factors that lead to the development of NODAT. We will also describe the impact of DM on the transplanted kidney, and the outcome of kidney-transplant recipients with NODAT. Additionally, we will present the most acceptable data on management of NODAT.

Evidence for rapamycin toxicity in pancreatic β-cells and a review of the underlying molecular mechanisms

Rapamycin is used frequently in both transplantation and oncology. Although historically thought to have little diabetogenic effect, there is growing evidence of β-cell toxicity. This Review draws evidence for rapamycin toxicity from clinical studies of islet and renal transplantation, and of rapamycin as an anticancer agent, as well as from experimental studies. Together, these studies provide evidence that rapamycin has significant detrimental effects on β-cell function and survival and peripheral insulin resistance. The mechanism of action of rapamycin is via inhibition of mammalian target of rapamycin (mTOR). This Review describes the complex mTOR signaling pathways, which control vital cellular functions including mRNA translation, cell proliferation, cell growth, differentiation, angiogenesis, and apoptosis, and examines molecular mechanisms for rapamycin toxicity in β-cells. These mechanisms include reductions in β-cell size, mass, proliferation and insulin secretion alongside increases in apoptosis, autophagy, and peripheral insulin resistance. These data bring into question the use of rapamycin as an immunosuppressant in islet transplantation and as a second-line agent in other transplant recipients developing new-onset diabetes after transplantation with calcineurin inhibitors. It also highlights the importance of close monitoring of blood glucose levels in patients taking rapamycin as an anticancer treatment, particularly those with preexisting glucose intolerance.

CRTC2 is required for β-cell function and proliferation

Previous work in insulinoma cell lines has established that calcineurin plays a critical role in the activation of cAMP-responsive element binding protein (Creb), a key transcription factor required for β-cell function and survival, by dephosphorylating the Creb coactivator Creb-regulated transcription coactivator (Crtc)2 at 2 regulatory sites, Ser171 and Ser275. Here, we report that Crtc2 is essential both for glucose-stimulated insulin secretion and cell survival in the β-cell. Endogenous Crtc2 activation is achieved via increasing glucose levels to the physiological feeding range, indicating that Crtc2 is a sensor that couples ambient glucose concentrations to Creb activity in the β-cell. Immunosuppressant drugs such as cyclosporin A and tacrolimus that target the protein phosphatase calcineurin are commonly administered after organ transplantation. Chronic use is associated with reduced insulin secretion and new onset diabetes, suggestive of pancreatic β-cell dysfunction. Importantly, we show that overexpression of a Crtc2 mutant rendered constitutively active by introduction of nonphosphorylatable alanine residues at Ser171 and Ser275 permits Creb target gene activation under conditions when calcineurin is inhibited. Taken together, these data suggest that promoting Crtc2-Creb activity is required for β-cell function and proliferation and promoting this pathway could ameliorate symptoms of new onset diabetes after transplantation.

A case of inoperable malignant insulinoma with resistant hypoglycemia who experienced the most significant clinical improvement with everolimus

Metastatic insulinomas may sometimes present with recurrent life-threatening hypoglycemia episodes. Such patients usually fail to respond to various therapeutic agents which causes constant dextrose infusion requirement. Herein, we present a resistant case of inoperable malignant insulinoma who was treated with many therapeutic agents and interventions including somatostatin analogues, Yttrium-90 radioembolization, everolimus, radiotherapy, and chemoembolization. Close blood sugar monitorization during these therapies showed the most favourable response with everolimus. Everolimus treatment resulted in rapid improvement of hypoglycemia episodes, letting us discontinue dextrose infusion and discharge the patient. However, experience with everolimus in such patients is still limited, and more precise data can be obtained with the increasing use of this agent for neuroendocrine tumours.

Efficacy of everolimus in patients with metastatic insulinoma and refractory hypoglycemia

BACKGROUND

Refractory hypoglycemia in patients with metastatic insulinoma is an important cause of morbidity and mortality. Everolimus could be a new therapeutic option.

METHODS

Within the French Group, we conducted a retrospective, multicentric study of endocrine tumors to evaluate the time to the first recurrence of symptomatic hypoglycemia, after everolimus initiation, in patients with metastatic insulinoma and refractory hypoglycemia. Ongoing hyperglycemic medical options, tumor response, and safety information were recorded.

RESULTS

Twelve patients with metastatic insulinoma and refractory hypoglycemia who were treated with everolimus between May 2007 and June 2011 were reviewed. Everolimus (starting dose, 10 mg/day, except in one patient, 5 mg/day) was given after a median of four previous therapeutic lines. Medication aimed at normalizing blood glucose levels in 11 patients. After a median duration of 6.5 months (range 1-35+ months), median time to the first recurrence of symptomatic hypoglycemia was 6.5 months (range 0 to 35+ months). Three patients discontinued everolimus because of cardiac and/or pulmonary adverse events at 1, 1.5, and 7 months after initiation, which led to two deaths. Three patients discontinued everolimus because of tumor progression at 2, 3, and 10 months after initiation, without recurrence of hypoglycemia.

CONCLUSION

Everolimus appears to be a new effective treatment for patients with metastatic insulinoma and refractory hypoglycemia. Tolerance should be carefully monitored.

Extracellular factors and immunosuppressive drugs influencing insulin secretion of murine islets

Approximately 60% of transplanted islets undergo apoptosis within the first week post-transplantation into the liver attributed to poor engraftment, immune rejection and toxicity of immunosuppressive drugs. Understanding how extracellular matrix (ECM) components, immunosuppressive drugs and proinflammatory cytokines affect insulin secretion will contribute to an improved clinical outcome of islet transplantations. In this study, functional activity of isolated murine islets was measured by glucose-stimulated insulin secretion (GSIS) and by electrophysiological measurements using patch-clamp. Cultivating islets with soluble fibronectin or laminin, as opposed to with coated laminin, markedly increased GSIS. Addition of cyclosporin A reduced GSIS and suppressed glucose-induced spike activity. Tacrolimus affected neither GSIS nor spike activity, indicating a different mechanism. To evaluate the influence of proinflammatory cytokines, islets were incubated with interleukin (IL)-1β, tumour necrosis factor (TNF)-α or with supernatants from cultured Kupffer cells, the main mediators of inflammation in the hepatic sinusoids. IL-1β exerted a bimodal effect on insulin secretion, stimulating below 2 ng/ml and suppressing above 10 ng/ml. Soluble laminin in combination with a stimulatory IL-1β concentration further increased insulin secretion by 20% compared to IL-1β alone, while with high IL-1β concentrations soluble laminin slightly attenuated GSIS inhibition. TNF-α alone did not affect GSIS, but with stimulatory IL-1β concentrations completely abolished it. Similarly, supernatants derived from Kupffer cells exerted a bimodal effect on GSIS. Our data suggest that improved insulin secretion of transplanted islets could be achieved by including soluble laminin and low IL-1β concentrations in the islet cultivation medium, and by a simultaneous inhibition of cytokine secretion from Kupffer cells.

In vitro effects of mycophenolic acid on survival, function, and gene expression of pancreatic beta-cells

Post-transplant diabetes mellitus represents an important complication of prolonged immunosuppressive treatment after solid organ transplantation. The immunosuppressive toxicity, responsible for a persistent impairment of glucose metabolism in pancreatic islet-transplanted patients, is mainly attributed to calcineurin inhibitors and steroids, while other immunosuppressive molecules (azathioprine and mycophenolic acid, MPA) are considered not to have a toxic effect. In the present study, in vitro effects of MPA have been investigated in mouse beta-cell lines (βTC-1 and βTC-6) and in purified human pancreatic islets. βTC-1, βTC-6, and human pancreatic islets were exposed to various concentrations of MPA for different times. Consequently, we evaluated the viability, the induction of apoptosis, the glucose-stimulated insulin secretion, and the expression of β-cell function genes (Isl1, Pax6, Glut-2, glucokinase) and apoptosis-related genes (Bax and Bcl2). βTC-1, βTC-6, and human islets treated, respectively, for 48 and 72 h with 15-30 nM MPA showed altered islet architecture, as compared with control cells. We observed for βTC-1 and βTC-6 almost 70% reduction in cell viability; three to sixfold induction of TUNEL/apoptotic-positive cells quantified by FACS analysis. A twofold increase in apoptotic cells was observed in human islets after MPA exposure associated with strong inhibition of glucose-stimulated insulin secretion. Furthermore, we showed significant down-regulation of gene expression of molecules involved in β-cell function and increase rate between Bax/Bcl2. Our data demonstrate that MPA has an in vitro diabetogenic effect interfering at multiple levels with survival and function of murine and human pancreatic β-cells.

Cellular and physiological mechanisms of new-onset diabetes mellitus after solid organ transplantation

New-onset diabetes after transplantation is recognized as one of the metabolic consequences which may increase the risk of morbidity and mortality after solid organ transplantation. The pathophysiology of new-onset diabetes after transplantation has not been clearly defined and may resemble that of Type 2 diabetes, characterized by predominantly insulin resistance or defective insulin secretion, or both. This review aims to summarize the current state of knowledge regarding the prevalence, consequences, pathogenesis, and management of new-onset diabetes after transplantation, with a major focus on the possible mechanisms involved in the pathogenesis of the disorder. The aetiology of new-onset diabetes after transplantation is multifactorial, with diabetogenic immunosuppressive drugs playing a major role. Multiple cellular and physiologic mechanisms are involved in the process. Selection of an appropriate maintenance immunosuppressive regimen should involve balancing the risk of patient and graft survival vs. the potential for new-onset diabetes after transplantation.

Association between a common KCNJ11 polymorphism (rs5219) and new-onset posttransplant diabetes in patients treated with Tacrolimus

KCNJ11 polymorphisms have been linked to the risk of developing type 2 diabetes. Our aim was to define the contribution of KCNJ11 to new-onset diabetes after transplantation (NODAT) among patients treated with Tacrolimus (Tac). A total of 115 NODAT and 205 non-NODAT were genotyped for rs5219 (p.E23K). AA+AG genotypes were significantly associated with NODAT-risk (p=0.004; OR=2.10). The reported effect of this KCNJ11 polymorphism on insulin release by beta cells could explain this association.

New therapeutic options for metastatic malignant insulinomas

Insulinomas are the most common, functioning, pancreatic neuroendocrine tumours. The great majority (>90%) of insulinomas are nonmetastatic at presentation and can be surgically cured. The <10% patients with distant (liver-bone) metastases have a median survival of < 2 years. Everolimus and sunitinib have been recently introduced as targeted therapies for metastatic pancreatic neuroendocrine tumours. An additional advantage of everolimus in the treatment of patients with metastatic insulinomas is its capability to increase blood glucose levels. Peptide receptor radiotherapy using radiolabelled somatostatin analogues has also been shown to be successful in controlling tumour growth of metastatic pancreatic neuroendocrine tumours. In patients with metastatic insulinomas, this therapeutic modality was also effective in controlling hypoglycaemia, even in the presence of tumour regrowth. With the introduction of these new therapeutic modalities, the therapeutic arsenal for the 'tailor-made' approach of patients with metastatic insulinomas is further expanded.

Rapamycin impairs proliferation of transplanted islet β cells

BACKGROUND

The cause for a progressive attrition of islet graft function observed over the years after islet transplantation is not well defined but may be in part the result of adverse effects of immunosuppressive agents. In this study, we examined the effect of rapamycin, a key component of the immunosuppressive regimen, on β-cell replication of transplanted islets.

METHODS

Mice transplanted with rat islets under kidney capsule received bromodeoxyuridine for 7 days. Mice were treated with rapamycin or appropriate vehicle. β-cell replication was determined by double immunofluorescence staining for insulin and bromodeoxyuridine. For in vitro studies, apoptosis, glucose-stimulated insulin secretion, and proliferation were determined in islet cells incubated with EdU in the presence or absence of rapamycin.

RESULTS

In our islet transplant model, rapamycin impaired glucose tolerance and β-cell proliferation of transplanted and host islets. In vitro, rapamycin reduced glucose-stimulated insulin secretion and reversibly decreased β-cell replication. The inhibitory effect of rapamycin on β-cell proliferation was not due to the decrease in insulin release. Additionally, in islet cells, expression of cell cycle proteins was significantly modified by rapamycin, suggesting a blockade of cell cycle progression. Inhibition of p38MAPK partially reverted rapamycin effect on β-cell proliferation.

CONCLUSION

Rapamycin, at concentration usually used to prevent islet graft rejection, is able to reduce the rate of β-cell proliferation in transplanted rat islets but also in host murine islets. These data suggest that the progressive islet graft dysfunction observed under immunosuppressive therapy may result in part from an impairment of β-cell regeneration.

Cyclosporin and tacrolimus impair insulin secretion and transcriptional regulation in INS-1E beta-cells

BACKGROUND AND PURPOSE

Introducing the calcineurin inhibitors cyclosporin (CsA) and tacrolimus (Tac) has improved the outcome of organ transplants, but complications such as new onset diabetes mellitus after transplantation (NODAT) decrease survival rates.

EXPERIMENTAL APPROACH

We sought, in a beta-cell culture model, to elucidate the pathogenic mechanisms behind NODAT and the relative contribution of the calcineurin inhibitors. INS-1E cells were incubated at basal and stimulatory glucose concentrations, while exposed to pharmacologically relevant doses of CsA, Tac and vehicle for 6 or 24 h.

RESULTS

Tac inhibited basal (P < 0.05), but not glucose-stimulated insulin secretion (GSIS) after 6 h of exposure. After 24 h, both agents inhibited basal and GSIS (P < 0.05). Calcineurin phosphatase activity was decreased by both drugs during all conditions. Apoptosis was only seen with CsA treatment, which also induced a slight suppression of calcineurin and insulin mRNA, as well as increased levels of the sterol receptor element binding protein (SREBP)-1c, a transcription factor thought to suppress genes essential for beta-cell function and induce insulin resistance. Expression levels of nuclear factor of activated T-cells (NFAT)-c1, -c2, -c3 and -c4 were not decreased notably by either drug.

CONCLUSIONS AND IMPLICATIONS

Tac had acute inhibitory effects on basal insulin secretion, but prolonged exposure (24 h) to Tac or CsA revealed similar suppression of insulin secretion. These prolonged effects were mirrored by a total inhibition of calcineurin activity in beta-cells. CsA showed greater inhibition of beta-cell survival and transcriptional markers, essential for beta-cell function.

Everolimus in the treatment of renal cell carcinoma and neuroendocrine tumors

Renal cell carcinoma (RCC) and neuroendocrine tumors (NET) are uncommon malignancies, highly resistant to chemotherapy, that have emerged as attractive platforms for evaluating novel targeted regimens. Everolimus is an oral rapamycin derivative within the mammalian target of rapamycin class of agents. Preclinical series have shown that everolimus exhibits anticancer effects in RCC and NET cell lines. A phase 3 placebo-controlled study in advanced clear-cell RCC, known as RECORD-1 (for "REnal Cell cancer treatment with Oral RAD001 given Daily"), documented that everolimus stabilizes tumor progression, prolongs progression-free survival and has acceptable tolerability in patients previously treated with the multikinase inhibitors sunitinib and/or sorafenib. Everolimus has been granted regulatory approval for use in sunitinib-pretreated and/or sorafenib-pretreated advanced RCC and incorporated into clinical practice guidelines, and the RECORD-1 safety data are being used to develop recommendations for managing clinically important adverse events in everolimus-treated patients. Ongoing clinical trials are evaluating everolimus as earlier RCC therapy (first-line for advanced disease and as neoadjuvant therapy), in non-clear-cell tumors, and in combination with various other approved or investigational targeted therapies for RCC. Regarding advanced NET, recently published phase 2 data support the ability of everolimus to improve disease control in patients with advanced NET as monotherapy or in combination with somatostatin analogue therapy, octreotide long-acting release (LAR). Forthcoming data from phase 3 placebo-controlled trials of everolimus, one focused on monotherapy for pancreatic NET and the other on combination use with octreotide LAR for patients with advanced NET and a history of carcinoid syndrome, will provide insight into its future place in NET therapy. The results of a number of ongoing phase 3 evaluations of everolimus will determine its broader applicability in treating breast cancer (in combination with chemotherapy and hormonal therapy), several advanced gastrointestinal cancers, hepatocellular carcinoma, and lymphoma (in the adjuvant setting), as well as the various lesions associated with the tuberous sclerosis complex tumor suppressor gene.

Tacrolimus causes a blockage of protein secretion which reinforces its immunosuppressive activity and also explains some of its toxic side-effects

BACKGROUND

Tacrolimus (FK506) is a macrolide immunosuppressant drug from the calcineurin inhibitor family, widely used in solid organ and islet cell transplantation, but produces significant side-effects.

OBJECTIVE

This study examined the effect of FK506 on interleukin-2 (IL-2) and insulin secretion, establishing a novel characteristic of this drug that could explain its diverse adverse effects, and developed an experimental model for the simultaneous analysis of mRNA expression and protein secretion affected by this drug.

METHODS

The IL-2 levels when tacrolimus was administered were analysed by Western blot, immunocytochemistry and RT-PCR in a T lymphocyte cellular line (Jurkat) 24 h post-stimulation. The insulin levels when tacrolimus was administered were analysed 4 h after stimulation of glucose-induced insulin secretion in a pancreatic cellular line (MIN6).

RESULTS

The previously published information describes tacrolimus as only capable of partially blocking IL-2 mRNA expression. In our hands, the cellular content of IL-2 is almost undetectable in stimulated Jurkat cells and can be detected in cellular extracts only when the secretory pathway is blocked by brefeldin A (BFA). BFA added 2 h after the beginning of stimulation was able to inhibit IL-2 secretion, without affecting IL-2 mRNA expression. Therefore BFA utilization allowed us to establish a model to analyze the effect on IL-2 secretion, separately from its expression. Tacrolimus added before stimulation inhibits only IL-2 synthesis, but blocks IL-2 protein secretion when added 2 h after stimulation. Similarly, tacrolimus is also capable of blocking the glucose-stimulated secretion of insulin by MIN6 cells. An increase of the intracellular content can be detected concomitantly with a decrease of the hormone measured in the culture medium.

CONCLUSIONS

Results of this study indicate that tacrolimus possesses another important effect in addition to the inhibition of IL-2 gene transcription, namely the ability to act as a general inhibitor of the protein secretory pathway. These results strongly suggest that the diabetogenic effect of the immune suppressant FK506 could be caused by the blockade of insulin secretion. This novel effect also provides an explanation for other side-effects observed in immunosuppressive treatment.

Calcineurin inhibitor effects on glucose metabolism and endothelial function following renal transplantation

BACKGROUND

Calcineurin inhibitors (CNI) are involved in the development of post-transplant diabetes mellitus (PTDM). Changes in insulin secretion and sensitivity contribute to the development of PTDM and are associated with endothelial function.

METHODS

In a pre-defined substudy of a previously published randomized trial in renal transplant recipients we compared the effect of CNI treatment (n = 23) with complete CNI-avoidance (n = 21) on insulin secretion and sensitivity (oral glucose tolerance test) as well as endothelial function (laser Doppler flowmetry), 10 wk and 12 months following transplantation.

RESULTS

Insulin sensitivity differed 10 wk post-transplant and was significantly better after 12 months in patients never treated with CNI drugs [0.091 (0.050) vs. 0.083 (0.036) micromol/kg/min/pmol/L, p = 0.043]. Insulin secretion tended to be higher in CNI treated patients at both time points (p = 0.068). Endothelial function was not significantly different at week 10 [540 (205) vs. 227 (565) arbitary units x minutes, p = 0.35] or month 12 [510 (620) vs. 243 (242), p = 0.33].

CONCLUSIONS

Findings in the present study indicate that long-term CNI treatment negatively affects glucose metabolism and this may contribute to the increased risk for premature cardiovascular disease in CNI treated renal transplant recipients. Further studies to elucidate this hypothesis are, however, needed.

Current status of islet cell transplantation

Despite substantial advances in islet isolation methods and immunosuppressive protocol, pancreatic islet cell transplantation remains an experimental procedure currently limited to the most severe cases of type 1 diabetes mellitus. The objectives of this treatment are to prevent severe hypoglycemic episodes in patients with hypoglycemia unawareness and to achieve a more physiological metabolic control. Insulin independence and long term-graft function with improvement of quality of life have been obtained in several international islet transplant centers. However, experimental trials of islet transplantation clearly highlighted several obstacles that remain to be overcome before the procedure could be proposed to a much larger patient population. This review provides a brief historical perspective of islet transplantation, islet isolation techniques, the transplant procedure, immunosuppressive therapy, and outlines current challenges and future directions in clinical islet transplantation.

Anti-proinflammatory effects of sirolimus on human islet preparations

BACKGROUND

Sirolimus plays a critical role in facilitating steroid-free immunosuppression, in conjunction with low dose tacrolimus, in current islet transplantation. Although several studies have investigated the effects of sirolimus on islet cells, conflicting results have been reported. In this study, we assessed the effects of sirolimus supplementation in culture media on human islet preparations, focusing on the anti-proinflammatory aspects.

METHODS

Human islet preparations were divided into four groups: pure (purity >90%) sirolimus (30 ng/mL); pure control (0 ng/mL); impure (purity 40%-60%) sirolimus; and impure control. All groups were cultured for 3 days and assessed regarding glucose stimulated insulin release, fractional beta-cell viability, beta-cell, and macrophage content. Cytokine and chemokine production from islet preparations and sorted pancreatic ductal cells were also examined.

RESULTS

Stimulated insulin release in the impure sirolimus group was significantly increased (P=0.024), as previously reported. Although fractional beta-cell viability showed no significant differences, beta-cell survival during culture significantly increased in impure sirolimus group when compared with the impure control group (P=0.015). Tumor necrosis factor-alpha, interleukin-1beta, monocyte chemotactic protein-1, and macrophage inflammatory protein-1beta production from the impure sirolimus group significantly decreased (P<0.05). Furthermore, tumor necrosis factor-alpha and macrophage inflammatory protein-1beta production from sorted ductal cells significantly decreased in the sirolimus group (P<0.05). The number of macrophages contained in islet preparations significantly decreased in the impure sirolimus group when compared with the impure control group (P<0.05).

CONCLUSIONS

Sirolimus improved not only stimulated insulin release, but also beta-cell survival during culture. The antiinflammatory effects of sirolimus also appear beneficial to islet cells in culture and may be a useful strategy in improving islet transplantation outcomes.

Effects of non-steroid immunosuppressive drugs on insulin secretion in transplantation

Post-transplantation diabetes (PTD) is a serious complication in organ transplantation: not only does it increase the risk of graft dysfunction; it also increases cardiovascular morbidity and mortality. PTD incidence is correlated with age, non-Caucasian ethnic background, a family history of diabetes, excess weight, hepatitis C infection and steroid boluses for potential rejection. Different mechanisms might explain post-transplantation glucose metabolism disorders: ischemia-reperfusion disorders, whether renal, hepatic or cardiac, are responsible for insulin-resistance, which is increased by post-transplantation steroids; the detrimental effect of non-steroid immunosuppressive drugs on insulin-secretion could also be involved, especially with calcineurin inhibitors. In vivo and in vitro studies have shown that tacrolimus has inhibitory effects on insulin-secretion, while these effects are less obvious for cyclosporin, and were mainly demonstrated in vitro. Mycophenolate has no overt effect on insulin-secretion. Sirolimus and everolimus, two mTOR inhibitors, have shown controversial results in this realm. The effects of sirolimus (most often studied mTOR inhibitor) appear to depend on serum levels, cell type (ss cell or cell line), species (human or animal) and also environmental nutrients. At therapeutic concentrations, a stimulatory effect on insulin secretion was observed on human beta cells. This might explain the success of islet cell transplantation with the Edmonton protocol. Finally, steroids are mainly detrimental because they accentuate insulin resistance whereas anticalcineurins, in particular tacrolimus, lower insulin synthesis.

Immunosuppressive drug-induced diabetes

Post-transplant diabetes mellitus (PTDM) has emerged as a major adverse effect of immunosuppressive drugs (ISD). As recipients of organ transplants survive longer, the complications of diabetes mellitus have assumed greater importance. The predominant factor for causing PTDM by corticosteroids seems to be the aggravation of insulin resistance, however several studies have displayed deleterious effects on insulin secretion and beta-cells. Calcineurin inhibitors induce PTDM by a number of mechanisms, including decreased insulin secretion and a direct toxic effect on the pancreatic beta-cells. Recent in vitro studies stress on the increased apoptosis of beta-cells when exposed to these drugs. Studies involving other immunosuppressive agents (mycophenolate mofetil [MMF], sirolimus) are scarcer and lead to conflicting results, while daclizumab seems to have a neutral effect. Clinical studies have consistently shown a greater potential of tacrolimus to induce PTDM compared with cyclosporine. Reducing PTDM incidence is a feasible goal while using corticosteroid-sparing regimens and/or lower tacrolimus trough levels. In patients developing PTDM, conversion from tacrolimus to cyclosporine could improve or reverse glucose tolerance abnormalities. In the absence of well-designed studies in this specific indication, treatment of PTDM is based on the same principles as type 2 diabetes mellitus. Thiazolidinediones do not display any pharmacological interaction with calcineurin inhibitors, but their safety and efficacy in PTDM need to be confirmed in large-scale randomized trials. Use of sulfonylureas has to be cautious regarding the suspected interaction of some of them with calcineurin inhibitors. If needed, insulin regimens have to be adapted in patients who display the particular glycaemic profile of corticosteroid-induced diabetes. Incretin-based therapies, due to their specific action on beta-cell apoptosis and proliferation, raise promises that have to be confirmed in clinical studies. Until methods for inducing specific graft tolerance become available, immunosuppressive regimens should be tailored to the individual patient on the basis of predictive criteria for the development of PTDM.

The impact of the mTOR inhibitor sirolimus on the proliferation and function of pancreatic islets and ductal cells

AIMS/HYPOTHESIS

The Edmonton Protocol for islet transplantation has provided hope for type 1 diabetic patients. However, this protocol requires lifelong immunosuppression, specifically sirolimus, a cellular antiproliferate. The effect of sirolimus on human pancreatic ductal cells (HDCs) is not known. This may be important since HDCs are believed to be islet precursors. Since neonatal porcine islets (NPIs), which contain many ductal precursor cells, could be a potential clinical source of islets, we also tested the effects of sirolimus on this tissue.

METHODS

HDCs (n=4), NPIs (n=9) and human islets (n=5) were cultured with and without sirolimus (20 ng/ml) for 6 days.

RESULTS

HDCs and NPIs cultured with sirolimus showed a 50 and 28% decrease, respectively, in cell number relative to control (p<0.05). Control cultures expanded 1.65- and 2.44-fold relative to time 0. Decreases in cell number of sirolimus-treated HDCs were not due to apoptosis as measured by TUNEL staining. No functional effects on human islets or NPIs were observed following static incubation with high glucose. Treatment of syngeneically transplanted and naïve BALC/c mice with sirolimus resulted in altered OGTT profiles with prolonged elevation of hyperglycaemia and weight gain. There was no difference in graft and organ insulin content between treatment groups.

CONCLUSIONS/INTERPRETATION

Our results indicate that sirolimus decreases ductal cell numbers in culture and alters glucose-stimulated insulin secretion in vivo. The administration of sirolimus to islet transplant recipients is likely to impair graft function as a result of decreasing ductal neogenesis and induction of insulin resistance.

Adenovirus-mediated XIAP gene transfer reverses the negative effects of immunosuppressive drugs on insulin secretion and cell viability of isolated human islets

Immunosuppressive drugs are routinely used to provide tolerance after whole pancreas and islet cell transplantations. While they are essential in inhibiting graft rejection, little is known about their effect on islet function and beta-cell viability. In this study, we report that tacrolimus, sirolimus, and mycophenolic acid, when added to cultures of freshly isolated human islets, induce a downregulation of the synthesis and secretion of insulin. These functional changes are associated with decreased islet cell viability. All three agents induce a decrease of intracellular levels of Bcl-2 and Bcl-xL, with an increased level of Smac, indicating that they are capable of promoting a downregulation of anti-apoptotic factors and an accumulation of pro-apoptotic mediators. Transduction of islet cells with the anti-apoptotic gene XIAP prevents the negative effects of these drugs on the function and viability of islets. XIAP-infected cells show a higher expression of phospho-CREB (cAMP-responsive element binding protein) and a reduced level of Smac, resulting in a significant reduction of apoptotic cells and a preservation of the glucose-dependent secretion of insulin. In conclusion, the present study demonstrates that genetically modified human islets expressing XIAP are resistant to the negative effects of immunosuppressive drugs on insulin secretion and cell viability.

Benefit-Risk Assessment of Sirolimus in Renal Transplantation

Sirolimus (rapamycin) is a macrocyclic lactone isolated from a strain of Streptomyces hygroscopicus that inhibits the mammalian target of rapamycin (mTOR)-mediated signal-transduction pathways, resulting in the arrest of cell cycle of various cell types, including T- and B-lymphocytes. Sirolimus has been demonstrated to prolong graft survival in various animal models of transplantation, ranging from rodents to primates for both heterotopic, as well as orthotopic organ grafting, bone marrow transplantation and islet cell grafting. In human clinical renal transplantation, sirolimus in combination with ciclosporin (cyclosporine) efficiently reduces the incidence of acute allograft rejection. Because of the synergistic effect of sirolimus on ciclosporin-induced nephrotoxicity, a prolonged combination of the two drugs inevitably leads to progressive irreversible renal allograft damage. Early elimination of calcineurin inhibitor therapy or complete avoidance of the latter by using sirolimus therapy is the optimal strategy for this drug. Prospective randomised phase II and III clinical studies have confirmed this approach, at least for recipients with a low to moderate immunological risk. For patients with a high immunological risk or recipients exposed to delayed graft function, sirolimus might not constitute the best therapeutic choice--despite its ability to enable calcineurin inhibitor sparing in the latter situation--because of its anti-proliferative effects on recovering renal tubular cells. Whether lower doses of sirolimus or a combination with a reduced dose of tacrolimus would be advantageous in these high risk situations remains to be determined. Clinically relevant adverse effects of sirolimus that require a specific therapeutic response or can potentially influence short- and long-term patient morbidity and mortality as well as graft survival include hypercholesterolaemia, hypertriglyceridaemia, infectious and non-infectious pneumonia, anaemia, lymphocele formation and impaired wound healing. These drug-related adverse effects are important determinants in the choice of a tailor-made immunosuppressive drug regimen that complies with the individual patient risk profile. Equally important in the latter decision is the lack of severe intrinsic nephrotoxicity associated with sirolimus and its advantageous effects on arterial hypertension, post-transplantation diabetes mellitus and esthetic changes induced by calcineurin inhibitors. Mild and transient thrombocytopenia, leukopenia, gastrointestinal adverse effects and mucosal ulcerations are all minor complications of sirolimus therapy that have less impact on the decision for choosing this drug as the basis for tailor-made immunosuppressive therapy. It is clear that sirolimus has gained a proper place in the present-day immunosuppressive armament used in renal transplantation and will contribute to the development of a tailor-made immunosuppressive therapy aimed at fulfilling the requirements outlined by the individual patient profile.

Cross-sectional and prospective association between proinsulin secretion and graft function after clinical islet transplantation

Proinsulin levels as a marker of beta-cell dysfunction have not been described after clinical islet transplantation. Proinsulin secretion was studied in 23 type 1 diabetic patients after islet allotransplantation and in 20 age-matched nondiabetic controls. Fasting serum insulin, total proinsulin (TP), intact proinsulin, proinsulin fragments (PFs) and their ratios to insulin were determined 1 and 12 months after patients became insulin independent. TP, PF, and proinsulin/insulin ratios were lower in transplant recipients compared with controls, in patients who retained long-term insulin independence. Insulin, C-peptide, and intact proinsulin values were similar in transplant recipients and controls. Hormone levels remained stable over time in the group of patients who retained long-term insulin independence, but the TP and PF levels were higher at 12 months compared with 1 month in the group of patients who resumed insulin therapy. TP and PF levels were reduced in transplant recipients compared with controls but increased over time if insulin independence was lost.

Pancreas transplantation: indications and consequences

Pancreas transplantation continues to evolve as a strategy in the management of diabetes mellitus. The first combined pancreas-kidney transplant was reported in 1967, but pancreas transplant now represents a number of procedures, each with different indications, risks, benefits, and outcomes. This review will summarize these procedures, including their risks and outcomes in comparison to kidney transplantation alone, and how or if they affect the consequences of diabetes: hyperglycemia, hypoglycemia, and microvascular and macrovascular complications. In addition, the new risks introduced by immunosuppression will be reviewed, including infections, cancer, osteoporosis, reproductive function, and the impact of immunosuppression medications on blood pressure, lipids, and glucose tolerance. It is imperative that an endocrinologist remain involved in the care of the pancreas transplant recipient, even when glucose is normal, because of the myriad of issues encountered post transplant, including ongoing management of diabetic complications, prevention of bone loss, and screening for failure of the pancreas graft with reinstitution of treatment when indicated. Although long-term patient and graft survival have improved greatly after pancreas transplant, a multidisciplinary team is needed to maximize long-term quality, as well as quantity, of life for the pancreas transplant recipient.

Role of calcium in pancreatic islet cell death by IFN-gamma/TNF-alpha

We studied the intracellular events associated with pancreatic beta cell apoptosis by IFN-gamma/TNF-alpha synergism. IFN-gamma/TNF-alpha treatment of MIN6N8 insulinoma cells increased the amplitude of high voltage-activated Ca(2+) currents, while treatment with IFN-gamma or TNF-alpha alone did not. Cytosolic Ca(2+) concentration ([Ca(2+)](c)) was also increased by IFN-gamma/TNF-alpha treatment. Blockade of L-type Ca(2+) channel by nifedipine abrogated death of insulinoma cells by IFN-gamma/TNF-alpha. Diazoxide that attenuates voltage-activated Ca(2+) currents inhibited MIN6N8 cell death by IFN-gamma/TNF-alpha, while glibenclamide that accentuates voltage-activated Ca(2+) currents augmented insulinoma cell death. A protein kinase C inhibitor attenuated MIN6N8 cell death and the increase in [Ca(2+)](c) by IFN-gamma/TNF-alpha. Following the increase in [Ca(2+)](c), calpain was activated, and calpain inhibitors decreased insulinoma cell death by IFN-gamma/TNF-alpha. As a downstream of calpain, calcineurin was activated and the inhibition of calcineurin activation by FK506 diminished insulinoma cell death by IFN-gamma/TNF-alpha. BAD phosphorylation was decreased by IFN-gamma/TNF-alpha because of the increased calcineurin activity, which was reversed by FK506. IFN-gamma/TNF-alpha induced cytochrome c translocation from mitochondria to cytoplasm and activation of caspase-9. Effector caspases such as caspase-3 or -7 were also activated by IFN-gamma/TNF-alpha treatment. These results indicate that IFN-gamma/TNF-alpha synergism induces pancreatic beta cell apoptosis by Ca(2+) channel activation followed by downstream intracellular events such as mitochondrial events and caspase activation and also suggest the therapeutic potential of Ca(2+) modulation in type 1 diabetes.

Regulation of ERK1 and ERK2 by glucose and peptide hormones in pancreatic beta cells

We showed previously that ERK1/2 were activated by glucose and amino acids in pancreatic beta cells. Here we examine and compare signaling events that are necessary for ERK1/2 activation by glucose and other stimuli in beta cells. We find that agents that interrupt Ca2+ signaling by a variety of mechanisms interfere with glucose- and glucagon-like peptide (GLP-1)-stimulated ERK1/2 activity. In particular, calmodulin antagonists, FK506, and cyclosporin, immunosuppressants that inhibit the calcium-dependent phosphatase calcineurin, suppress ERK1/2 activation by both glucose and GLP-1. Ca2+ signaling from intracellular stores is also essential for ERK1/2 activation, because thapsigargin blocks ERK1/2 activation by glucose or GLP-1. The glucose-sensitive mechanism is distinct from that used by phorbol ester or insulin to stimulate ERK1/2 but shares common features with that used by GLP-1.