Hyperinsulinism in Infancy: From Basic Science to Clinical Disease

Oxidant-induced disruption of vascular K+ channel function: implications for diabetic vasculopathy

Diabetes in humans a chronic metabolic disorder characterised by hyperglycaemia, it is associated with an increased risk of cardiovascular disease, disruptions to metabolism and vascular functions. It is also linked to oxidative stress and its complications. Its role in vascular dysfunctions is generally reported without detailed impact on the molecular mechanisms. Potassium ion channel (K+ channels) are key regulators of vascular tone, and as membrane proteins, are modifiable by oxidant stress associated with diabetes. This review manuscript examined the impact of oxidant stress on vascular K+ channel functions in diabetes, its implication in vascular complications and metabolic and cardiovascular diseases.

Sequential Dearomatization/Rearrangement of Quinazoline-Derived Azomethine Imines for the Synthesis of Nitrogen-Rich Three-Dimensional Cage-Like Molecules

A sequential dearomatization/rearrangement reaction between quinazoline-derived azomethine imines and crotonate sulfonium salts has been developed to provide a series of three-dimensional cage-like molecules. The reaction involves two dearomatizations, two cyclizations, and two C-C bond and three C-N bond formations in one step. The new transformation has a broad substrate scope, does not require any added reagents, and proceeds under room temperature in a short time. A mechanistic rationale for the sequential dearomatization/rearrangement is also presented. Furthermore, the synthetic compounds are evaluated for their glucose control effect. Compounds 3aa and 3aj were found to be hyperglycemic, which might be lead compounds for treating hypoglycemia.

A loss-of-function mutation in KCNJ11 causing sulfonylurea-sensitive diabetes in early adult life

AIMS/HYPOTHESIS

The ATP-sensitive potassium (KATP) channel couples beta cell electrical activity to glucose-stimulated insulin secretion. Loss-of-function mutations in either the pore-forming (inwardly rectifying potassium channel 6.2 [Kir6.2], encoded by KCNJ11) or regulatory (sulfonylurea receptor 1, encoded by ABCC8) subunits result in congenital hyperinsulinism, whereas gain-of-function mutations cause neonatal diabetes. Here, we report a novel loss-of-function mutation (Ser118Leu) in the pore helix of Kir6.2 paradoxically associated with sulfonylurea-sensitive diabetes that presents in early adult life.

METHODS

A 31-year-old woman was diagnosed with mild hyperglycaemia during an employee screen. After three pregnancies, during which she was diagnosed with gestational diabetes, the patient continued to show elevated blood glucose and was treated with glibenclamide (known as glyburide in the USA and Canada) and metformin. Genetic testing identified a heterozygous mutation (S118L) in the KCNJ11 gene. Neither parent was known to have diabetes. We investigated the functional properties and membrane trafficking of mutant and wild-type KATP channels in Xenopus oocytes and in HEK-293T cells, using patch-clamp, two-electrode voltage-clamp and surface expression assays.

RESULTS

Functional analysis showed no changes in the ATP sensitivity or metabolic regulation of the mutant channel. However, the Kir6.2-S118L mutation impaired surface expression of the KATP channel by 40%, categorising this as a loss-of-function mutation.

CONCLUSIONS/INTERPRETATION

Our data support the increasing evidence that individuals with mild loss-of-function KATP channel mutations may develop insulin deficiency in early adulthood and even frank diabetes in middle age. In this case, the patient may have had hyperinsulinism that escaped detection in early life. Our results support the importance of functional analysis of KATP channel mutations in cases of atypical diabetes.

Functional characterization of inactivating ABCC8 variants causing congenital hyperinsulinism

Congenital hyperinsulinism (CHI; OMIM: 256450) is characterized by persistent insulin secretion despite severe hypoglycemia. The most common causes are variants in the ATP-binding cassette subfamily C member 8(ABCC8) and potassium inwardly-rectifying channel subfamily J member 11(KCNJ11) genes. These encode ATP-sensitive potassium (KATP) channel subunit sulfonylurea receptor 1 (SUR1) and inwardly rectifying potassium channel (Kir6.2) proteins. A 7-day-old male infant presented with frequent hypoglycemic episodes and was clinically diagnosed with CHI, underwent trio-whole-exome sequencing, revealing compound heterozygous ABCC8 variants (c.307C>T, p.His103Tyr; and c.3313_3315del, p.Ile1105del) were identified. In human embryonic kidney 293 (HEK293) and rat insulinoma cells (INS-1) transfected with wild-type and variant plasmids, KATP channels formed by p.His103Tyr were delivered to the plasma membrane, whereas p.Ile1105del or double variants (p.His103Tyr coupled with p.Ile1105del) failed to be transported to the plasma membrane. Compared to wild-type channels, the channels formed by the variants (p.His103Tyr; p.Ile1105del) had elevated basal [Ca2+]i, but did not respond to stimulation by glucose. Our results provide evidence that the two ABCC8 variants may be related to CHI owing to defective trafficking and dysfunction of KATP channels.

Optimization of a Glucagon-Like Peptide 1 Receptor Antagonist Antibody for Treatment of Hyperinsulinism

Congenital hyperinsulinism (HI) is a genetic disorder in which pancreatic β-cell insulin secretion is excessive and results in hypoglycemia that, without treatment, can cause brain damage or death. Most patients with loss-of-function mutations in ABCC8 and KCNJ11, the genes encoding the β-cell ATP-sensitive potassium channel (KATP), are unresponsive to diazoxide, the only U.S. Food and Drug Administration-approved medical therapy and require pancreatectomy. The glucagon-like peptide 1 receptor (GLP-1R) antagonist exendin-(9-39) is an effective therapeutic agent that inhibits insulin secretion in both HI and acquired hyperinsulinism. Previously, we identified a highly potent antagonist antibody, TB-001-003, which was derived from our synthetic antibody libraries that were designed to target G protein-coupled receptors. Here, we designed a combinatorial variant antibody library to optimize the activity of TB-001-003 against GLP-1R and performed phage display on cells overexpressing GLP-1R. One antagonist, TB-222-023, is more potent than exendin-(9-39), also known as avexitide. TB-222-023 effectively decreased insulin secretion in primary isolated pancreatic islets from a mouse model of hyperinsulinism, Sur1-/- mice, and in islets from an infant with HI, and increased plasma glucose levels and decreased the insulin to glucose ratio in Sur1-/- mice. These findings demonstrate that targeting GLP-1R with an antibody antagonist is an effective and innovative strategy for treatment of hyperinsulinism.

ARTICLE HIGHLIGHTS

Patients with the most common and severe form of diazoxide-unresponsive congenital hyperinsulinism (HI) require a pancreatectomy. Other second-line therapies are limited in their use because of severe side effects and short half-lives. Therefore, there is a critical need for better therapies. Studies with the glucagon-like peptide 1 receptor (GLP-1R) antagonist, avexitide (exendin-(9-39)), have demonstrated that GLP-1R antagonism is effective at lowering insulin secretion and increasing plasma glucose levels. We have optimized a GLP-1R antagonist antibody with more potent blocking of GLP-1R than avexitide. This antibody therapy is a potential novel and effective treatment for HI.

Hypoglycemia in Children: Major Endocrine-Metabolic Causes and Novel Therapeutic Perspectives

Hypoglycemia is due to defects in the metabolic systems involved in the transition from the fed to the fasting state or in the hormone control of these systems. In children, hypoglycemia is considered a metabolic-endocrine emergency, because it may lead to brain injury, permanent neurological sequelae and, in rare cases, death. Symptoms are nonspecific, particularly in infants and young children. Diagnosis is based on laboratory investigations during a hypoglycemic event, but it may also require biochemical tests between episodes, dynamic endocrine tests and molecular genetics. This narrative review presents the age-related definitions of hypoglycemia, its pathophysiology and main causes, and discusses the current diagnostic and modern therapeutic approaches.

A novel mutation in the KCNJ11 gene (p.Val36Glu), predisposes to congenital hyperinsulinemia

The hypoglycemia induced by insulin hypersecretion in congenital hyperinsulinemia (CHI), a rare life-threatening condition can lead to irreversible brain damage in neonates. Inactivating mutations in the genes encoding K_ATP channel (ABCC8 and KCNJ11) as well as HNF4A, HNF1A, HADH, UCP2, and activating mutations in GLUD1, GCK, and SLC16A1 have been identified as causal. A 3-month-old male infant presenting tonic-clonic seizures and hyperinsulinemia was clinically assessed and subjected to genetic analysis. Besides the index patient, his parents were clinically investigated, and a detailed family history was also recorded. The laboratory investigations and the genetic test results of the parents were compared with the index patient. The biochemical and hormonal profile of the patient confirmed his suffering from CHI and did not respond to diazoxide treatment. The genetic testing revealed that the subject harbored a novel homozygous missense mutation in the KCNJ11 gene, (c.107T>A, p.Val36Glu.). The bioinformatic analysis revealed that valine is highly conserved and predicted that the variant allele (p.Val36Glu) is likely pathogenic and causal for CHI. Parents were heterozygous carriers and did not report any abnormal metabolic profile. Identification of such mutations is critical and likely to change the therapeutic interventions for such patients in the future.

Structural Insights into ATP-Sensitive Potassium Channel Mechanics: A Role of Intrinsically Disordered Regions

Commonly used techniques, such as CryoEM or X-ray, are not able to capture the structural reorganizations of disordered regions of proteins (IDR); therefore, it is difficult to assess their functions in proteins based exclusively on experiments. To fill this gap, we used computational molecular dynamics (MD) simulation methods to capture IDR dynamics and trace biological function-related interactions in the Kir6.2/SUR1 potassium channel. This ATP-sensitive octameric complex, one of the critical elements in the insulin secretion process in human pancreatic β-cells, has four to five large, disordered fragments. Using unique MD simulations of the full Kir6.2/SUR1 channel complex, we present an in-depth analysis of the dynamics of the disordered regions and discuss the possible functions they could have in this system. Our MD results confirmed the crucial role of the N-terminus of the Kir6.2 fragment and the L0-loop of the SUR1 protein in the transfer of mechanical signals between domains that trigger insulin release. Moreover, we show that the presence of IDRs affects natural ligand binding. Our research takes us one step further toward understanding the action of this vital complex.

A novel glucagon analog with an extended half-life, HM15136, normalizes glucose levels in rodent models of congenital hyperinsulinism

Congenital hyperinsulinism (CHI) is a rare genetic condition characterized by uncontrolled insulin secretion, resulting in hypoglycemia. Although glucagon has lately been regarded as a therapeutic option for CHI, its use is severely hampered by its poor solubility and stability at physiological pH, as well as its short duration of action. To address these constraints, we developed HM15136, a novel long-acting glucagon analog composed of a glucagon analog conjugated to the Fc fragment of human immunoglobulin G4 via a polyethylene glycol linker. In this study, we established that HM15136 was more soluble than natural glucagon (≥ 150 mg/mL vs 0.03 mg/mL). Next, we confirmed that HM15136 activated glucagon receptor in vitro and induced glycogenolysis and gluconeogenesis in rat primary hepatocytes. Pharmacokinetics (PK)/Pharmacodynamics (PD) analysis of HM15136 shows that HM15136 has a markedly longer half-life (36 h vs. < 5 min) and increased bioavailability (90%) compared to native glucagon in mice. Further, HM15136 could effectively reverse acute hypoglycemia induced by insulin challenge, and multiple doses of HM15136 could sustain increased blood glucose levels in CHI rats. In conclusion, our findings indicate that HM15136 promotes sustained elevation of blood glucose, demonstrating the potential for development as a once-weekly therapy for CHI.

Congenital Hyperinsulinism International: A Community Focused on Improving the Lives of People Living With Congenital Hyperinsulinism

Congenital hyperinsulinism (HI) is a rare disease affecting newborns. HI causes severe hypoglycemia due to the overproduction of insulin. The signs and symptoms of hypoglycemia in HI babies is often not discovered until brain damage has already occurred. Prolonged hypoglycemia from HI can even lead to death. Disease management is often complex with a high burden on caregivers. Treatment options are extremely limited and often require long hospital stays to devise. Cascading from suboptimal treatments and diagnostic practices are a host of other problems and challenges that many with HI and their families experience including continued fear of hypoglycemia and feeding problems. The aim of this paper is (1) to describe the current challenges of living with HI including diagnosis and disease management told from the perspective of people who live with the condition (2), to provide family stories of life with HI, and (3) to share how a rare disease patient organization, Congenital Hyperinsulinism International (CHI) is working to improve the lives of HI patients and their families. CHI is a United States based nonprofit organization with a global focus. The paper communicates the programs the patient advocacy organization has put into place to support HI families through its virtual and in-person gatherings. The organization also helps individuals access diagnostics, medical experts, and treatments. CHI also raises awareness of HI to improve patient outcomes with information about HI and prolonged hypoglycemia in twenty-three languages. CHI drives innovation for new and better treatments by funding research pilot grants, conducting research through the HI Global Registry, and providing patient experience expertise to researchers developing new treatments. The organization is also the sponsor of the CHI Collaborative Research Network which brings medical and scientific experts together for the development of a patient-focused prioritized research agenda.

Congenital Hyperinsulinism Caused by Novel Homozygous KATP Channel Gene Variants May Be Linked to Unexplained Neonatal Deaths among Kurdish Consanguineous Families

INTRODUCTION

Neonatal hypoglycemia due to congenital hyperinsulinism (CHI) is a potentially life-threatening condition. Biallelic pathogenic variants in KATP channel subunit genes (ABCC8, KCNJ11), causing severe forms of CHI, are more prevalent in regions with a significant rate of consanguinity and may lead to unexplained neonatal deaths. We hypothesized that KATP channel gene variants are the cause of CHI in three unrelated children from consanguineous Kurdish families with histories of four unexplained neonatal deaths with convulsions.

CASES

(1) A girl presented on the 6th day of life with recurrent hypoglycemic convulsions (blood glucose 2.05 mmol/L, insulin 58 mIU/L, C-peptide 2,242 pmol/L). (2) A girl with severe developmental delay was diagnosed with CHI at 3 years of age (blood glucose 2.78 mmol/L, insulin 8.1 mIU/L, C-peptide 761 pmol/L) despite a history of recurrent hypoglycemia since neonatal age. (3) A girl presented at 3 weeks of age with convulsions and unconsciousness (blood glucose 2.5 mmol/L, insulin 14.6 mIU/L, C-peptide 523 pmol/L). Coding regions of the ABCC8 and KCNJ11 genes were tested by Sanger sequencing. Potential variants were evaluated using the American College of Medical Genetics standards. Three novel causative homozygous variants were found - p.Trp514Ter in the ABCC8 gene (Pt2), and p.Met1Val (Pt1) and p.Tyr26Ter (Pt3) in the KCNJ11 gene.

CONCLUSION

CHI caused by KATP channel variants was elucidated in three children, providing a highly probable retrospective diagnosis for their deceased siblings. Future lives can be saved by timely diagnosis of CHI when encountering a neonate with unexplained seizures or other signs of recurrent and/or persistent hypoglycemia.

Congenital Hyperinsulinism

Hyperinsulinemic hypoglycemia (HH) is fairly common in neonates, particularly those born to diabetic mothers and those who are either large or small for gestational age. Immediate management of the disease focuses on achieving normoglycemia through frequent high-calorie feedings and/or intravenous glucose administration. Glucagon may be used for unstable infants in whom intravenous access cannot be obtained and enteral feedings cannot be administered. HH that persists despite these interventions should raise concern for congenital hyperinsulinism (CHI), prompting clinicians to perform a thorough evaluation. CHI consists of a group of genetic disorders in which inappropriate insulin secretion results in persistent hypoglycemia. Defects can occur in the various genes that regulate the pathway for insulin secretion in the pancreatic β-cells. Pharmacologic therapies are used for long-term management of the disease coupled with either curative or therapeutic surgical intervention. Because of the developing brain's high demand for glucose, these infants are at increased risk for hypoglycemic brain injury. This review will describe the pathogenesis of CHI, outlining the more common genetic mutations and associated syndromes. We will also discuss the clinical presentation, diagnosis, and management of CHI while providing insight into the overall prognosis.

Structure based analysis of KATP channel with a DEND syndrome mutation in murine skeletal muscle

Developmental delay, epilepsy, and neonatal diabetes (DEND) syndrome, the most severe end of neonatal diabetes mellitus, is caused by mutation in the ATP-sensitive potassium (K_ATP) channel. In addition to diabetes, DEND patients present muscle weakness as one of the symptoms, and although the muscle weakness is considered to originate in the brain, the pathological effects of mutated K_ATP channels in skeletal muscle remain elusive. Here, we describe the local effects of the K_ATP channel on muscle by expressing the mutation present in the K_ATP channels of the DEND syndrome in the murine skeletal muscle cell line C2C12 in combination with computer simulation. The present study revealed that the DEND mutation can lead to a hyperpolarized state of the muscle cell membrane, and molecular dynamics simulations based on a recently reported high-resolution structure provide an explanation as to why the mutation reduces ATP sensitivity and reveal the changes in the local interactions between ATP molecules and the channel.

Potassium (K+) channels in the pulmonary vasculature: Implications in pulmonary hypertension Physiological, pathophysiological and pharmacological regulation

The large K⁺ channel functional diversity in the pulmonary vasculature results from the multitude of genes expressed encoding K⁺ channels, alternative RNA splicing, the post-transcriptional modifications, the presence of homomeric or heteromeric assemblies of the pore-forming α-subunits and the existence of accessory β-subunits modulating the functional properties of the channel. K⁺ channels can also be regulated at multiple levels by different factors controlling channel activity, trafficking, recycling and degradation. The activity of these channels is the primary determinant of membrane potential (Em) in pulmonary artery smooth muscle cells (PASMC), providing an essential regulatory mechanism to dilate or contract pulmonary arteries (PA). K⁺ channels are also expressed in pulmonary artery endothelial cells (PAEC) where they control resting Em, Ca²⁺ entry and the production of different vasoactive factors. The activity of K⁺ channels is also important in regulating the population and phenotype of PASMC in the pulmonary vasculature, since they are involved in cell apoptosis, survival and proliferation. Notably, K⁺ channels play a major role in the development of pulmonary hypertension (PH). Impaired K⁺ channel activity in PH results from: 1) loss of function mutations, 2) downregulation of its expression, which involves transcription factors and microRNAs, or 3) decreased channel current as a result of increased vasoactive factors (e.g., hypoxia, 5-HT, endothelin-1 or thromboxane), exposure to drugs with channel-blocking properties, or by a reduction in factors that positively regulate K⁺ channel activity (e.g., NO and prostacyclin). Restoring K⁺ channel expression, its intracellular trafficking and the channel activity is an attractive therapeutic strategy in PH.

Glucose-induced insulin secretion in isolated human islets: Does it truly reflect β-cell function in vivo?

BACKGROUND

Diabetes always involves variable degrees of β-cell demise and malfunction leading to insufficient insulin secretion. Besides clinical investigations, many research projects used rodent islets to study various facets of β-cell pathophysiology. Their important contributions laid the foundations of steadily increasing numbers of experimental studies resorting to isolated human islets.

SCOPE OF REVIEW

This review, based on an analysis of data published over 60 years of clinical investigations and results of more recent studies in isolated islets, addresses a question of translational nature. Does the information obtained in vitro with human islets fit with our knowledge of insulin secretion in man? The aims are not to discuss specificities of pathways controlling secretion but to compare qualitative and quantitative features of glucose-induced insulin secretion in isolated human islets and in living human subjects.

MAJOR CONCLUSIONS

Much of the information gathered in vitro can reliably be translated to the in vivo situation. There is a fairly good, though not complete, qualitative and quantitative coherence between insulin secretion rates measured in vivo and in vitro during stimulation with physiological glucose concentrations, but the concordance fades out under extreme conditions. Perplexing discrepancies also exist between insulin secretion in subjects with Type 2 diabetes and their islets studied in vitro, in particular concerning the kinetics. Future projects should ascertain that the experimental conditions are close to physiological and do not alter the function of normal and diabetic islets.

Gs/Gq signaling switch in β cells defines incretin effectiveness in diabetes

By restoring glucose-regulated insulin secretion, glucagon-like peptide-1-based (GLP-1-based) therapies are becoming increasingly important in diabetes care. Normally, the incretins GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) jointly maintain normal blood glucose levels by stimulation of insulin secretion in pancreatic β cells. However, the reason why only GLP-1-based drugs are effective in improving insulin secretion after presentation of diabetes has not been resolved. ATP-sensitive K+ (KATP) channels play a crucial role in coupling the systemic metabolic status to β cell electrical activity for insulin secretion. Here, we have shown that persistent membrane depolarization of β cells due to genetic (β cell-specific Kcnj11-/- mice) or pharmacological (long-term exposure to sulfonylureas) inhibition of the KATP channel led to a switch from Gs to Gq in a major amplifying pathway of insulin secretion. The switch determined the relative insulinotropic effectiveness of GLP-1 and GIP, as GLP-1 can activate both Gq and Gs, while GIP only activates Gs. The findings were corroborated in other models of persistent depolarization: a spontaneous diabetic KK-Ay mouse and nondiabetic human and mouse β cells of pancreatic islets chronically treated with high glucose. Thus, a Gs/Gq signaling switch in β cells exposed to chronic hyperglycemia underlies the differential insulinotropic potential of incretins in diabetes.

Necrotizing Enterocolitis in Neonates With Hyperinsulinemic Hypoglycemia Treated With Diazoxide

The most common cause of persistent hypoglycemia in the neonatal period is hyperinsulinism. Severe, refractory hypoglycemia resulting from hyperinsulinism can lead to significant brain injury and permanent cognitive disability. Diazoxide is the first-line and only US Food and Drug Administration-approved, pharmacologic treatment for refractory hyperinsulinism. In recent years, the use of diazoxide in neonates with persistent hyperinsulinemic hypoglycemia has increased in the United States. Known adverse effects of diazoxide include fluid retention, hypertrichosis, neutropenia, thrombocytopenia, and more recently, pulmonary hypertension. It is currently unknown if diazoxide exposure is associated with an increased risk of necrotizing enterocolitis (NEC) in neonates. We reviewed the cases of 24 patients in a level IV NICU at Massachusetts General Hospital who received diazoxide over 12 years (April 2006-April 2018). All 24 patients received enteral diazoxide for refractory hyperinsulinemic hypoglycemia. A total of 5 patients developed NEC after initiation of diazoxide based on clinical and radiographic findings, corresponding to 20% of infants exposed to diazoxide. This is above our baseline incidence of NEC (1% for all inborn infants and 6% for all inborn very low birth weight infants). More research and monitoring are necessary to characterize the potential risk of NEC associated with the use of diazoxide in the neonatal period.

Structural Determinants of Insulin Release: Disordered N-Terminal Tail of Kir6.2 Affects Potassium Channel Dynamics through Interactions with Sulfonylurea Binding Region in a SUR1 Partner

Inward rectifying potassium ion channels (KATP), sensitive to the ATP/ADP concentration ratio, play an important, control role in pancreatic β cells. The channels close upon the increase of this ratio, which, in turn, triggers insulin release to blood. Numerous mutations in KATP lead to severe and widespread medical conditions such as diabetes. The KATP system consists of a pore made of four Kir6.2 subunits and four accompanying large SUR1 proteins belonging to the ABCC transporters group. How SUR1 affects KATP function is not yet known; therefore, we created simplified models of the Kir6.2 tetramer based on recently determined cryo-EM KATP structures. Using all-atom molecular dynamics (MD) with the CHARMM36 force field, targeted MD, and molecular docking, we revealed functionally important rearrangements in the Kir6.2 pore, induced by the presence of the SUR1 protein. The cytoplasmic domain of Kir6.2 (CTD) is brought closer to the membrane due to interactions with SUR1. Each Kir6.2 subunit has a conserved, functionally important, disordered N-terminal tail. Using molecular docking, we found that the Kir6.2 tail easily docks to the sulfonylurea drug binding region located in the adjacent SUR1 protein. We reveal, for the first time, dynamical behavior of the Kir6.2/SUR1 system, confirming a physiological role of the Kir6.2 disordered tail, and we indicate structural determinants of KATP-dependent insulin release from pancreatic β cells.

Ion Channels as Therapeutic Targets for Type 1 Diabetes Mellitus

Ion channels are integral proteins expressed in almost all living cells and are involved in muscle contraction and nutrient transport. They play a critical role in the normal functioning of the excitable tissues of the nervous system and regulate the action potential and contraction events. Dysfunction of genes encodes ion channel proteins, which disrupt the channel function and lead to a number of diseases, among which is type 1 diabetes mellitus (T1DM). Therefore, understanding the complex mechanism of ion channel receptors is necessary to facilitate the diagnosis and management of treatment. In this review, we summarize the mechanism of important ion channels and their potential role in the regulation of insulin secretion along with the limitations of ion channels as therapeutic targets. Furthermore, we discuss the recent investigations of the mechanism regulating the ion channels in pancreatic beta cells, which suggest that ion channels are active participants in the regulation of insulin secretion.

Possible New Strategies for the Treatment of Congenital Hyperinsulinism

OBJECTIVE

Congenital hyperinsulinism (CHI) is a rare disease characterized by persistent hypoglycemia as a result of inappropriate insulin secretion, which can lead to irreversible neurological defects in infants. Poor efficacy and strong adverse effects of the current medications impede successful treatment. The aim of the study was to investigate new approaches to silence β-cells and thus attenuate insulin secretion.

RESEARCH DESIGN AND METHODS

In the scope of our research, we tested substances more selective and more potent than the gold standard diazoxide that also interact with neuroendocrine ATP-sensitive K⁺ (K_ATP) channels. Additionally, K_ATP channel-independent targets as Ca²⁺-activated K⁺ channels of intermediate conductance (K_Ca3.1) and L-type Ca²⁺ channels were investigated. Experiments were performed using human islet cell clusters isolated from tissue of CHI patients (histologically classified as pathological) and islet cell clusters obtained from C57BL/6N (WT) or SUR1 knockout (SUR1^-/-) mice. The cytosolic Ca²⁺ concentration ([Ca²⁺]_c) was used as a parameter for the pathway regulated by electrical activity and was determined by fura-2 fluorescence. The mitochondrial membrane potential (ΔΨ) was determined by rhodamine 123 fluorescence and single channel currents were measured by the patch-clamp technique.

RESULTS

The selective K_ATP channel opener NN414 (5 µM) diminished [Ca²⁺]_c in isolated human CHI islet cell clusters and WT mouse islet cell clusters stimulated with 10 mM glucose. In islet cell clusters lacking functional K_ATP channels (SUR1^-/-) the drug was without effect. VU0071063 (30 µM), another K_ATP channel opener considered to be selective, lowered [Ca²⁺]_c in human CHI islet cell clusters. The compound was also effective in islet cell clusters from SUR1^-/- mice, showing that [Ca²⁺]_c is influenced by additional effects besides K_ATP channels. Contrasting to NN414, the drug depolarized ΔΨ in murine islet cell clusters pointing to severe interference with mitochondrial metabolism. An opener of K_Ca3.1 channels, DCEBIO (100 µM), significantly decreased [Ca²⁺]_c in SUR1^-/- and human CHI islet cell clusters. To target L-type Ca²⁺ channels we tested two already approved drugs, dextromethorphan (DXM) and simvastatin. DXM (100 µM) efficiently diminished [Ca²⁺]_c in stimulated human CHI islet cell clusters as well as in stimulated SUR1^-/- islet cell clusters. Similar effects on [Ca²⁺]_c were observed in experiments with simvastatin (7.2 µM).

CONCLUSIONS

NN414 seems to provide a good alternative to the currently used K_ATP channel opener diazoxide. Targeting K_Ca3.1 channels by channel openers or L-type Ca²⁺ channels by DXM or simvastatin might be valuable approaches for treatment of CHI caused by mutations of K_ATP channels not sensitive to K_ATP channel openers.

Increased proliferation and altered cell cycle regulation in pancreatic stem cells derived from patients with congenital hyperinsulinism

Congenital hyperinsulinism (CHI) is characterised by inappropriate insulin secretion causing profound hypoglycaemia and brain damage if inadequately controlled. Pancreatic tissue isolated from patients with diffuse CHI shows abnormal proliferation rates, the mechanisms of which are not fully resolved. Understanding cell proliferation in CHI may lead to new therapeutic options, alongside opportunities to manipulate β-cell mass in patients with diabetes. We aimed to generate cell-lines from CHI pancreatic tissue to provide in vitro model systems for research. Three pancreatic mesenchymal stem cell-lines (CHIpMSC1-3) were derived from patients with CHI disease variants: focal, atypical and diffuse. All CHIpMSC lines demonstrated increased proliferation compared with control adult-derived pMSCs. Cell cycle alterations including increased CDK1 levels and decreased p27^Kip1 nuclear localisation were observed in CHIpMSCs when compared to control pMSCs. In conclusion, CHIpMSCs are a useful in vitro model to further understand the cell cycle alterations leading to increased islet cell proliferation in CHI.

aThe characteristics of glucose metabolism in the sulfonylurea receptor 1 knockout rat model

Background

Sulfonylurea receptor 1 (SUR1) is primarily responsible for glucose regulation in normal conditions. Here, we sought to investigate the glucose metabolism characteristics of SUR1^−/− rats.

Methods

The TALEN technique was used to construct a SUR1 gene deficiency rat model. Rats were grouped by SUR1 gene knockout or not and sex difference. Body weight; glucose metabolism indicators, including IPGTT, IPITT, glycogen contents and so on; and other molecule changes were examined.

Results

Insulin secretion was significantly inhibited by knocking out the SUR1 gene. SUR1^−/− rats showed lower body weights compared to wild-type rats, and even SUR1^−/− males weighed less than wild-type females. Upon SUR1 gene knockout, the rats showed a peculiar plasma glucose profile. During IPGTT, plasma glucose levels were significantly elevated in SUR1^−/− rats at 15 min, which could be explained by SUR1 mainly working in the first phase of insulin secretion. Moreover, SUR1^−/− male rats showed obviously impaired glucose tolerance than before and a better insulin sensitivity in the 12th week compared with females, which might be related with excess androgen secretion in adulthood. Increased glycogen content and GLUT4 expression and the inactivation of GSK3 were also observed in SUR1^−/− rats, which suggested an enhancement of insulin sensitivity.

Conclusions

These results reconfirm the role of SUR1 in systemic glucose metabolism. More importantly, our SUR1^−/− rat model might be applied in other fields, such as for exploring other hypoglycaemic functions of sulfonylureas.

Electronic supplementary material

The online version of this article (10.1186/s10020-018-0067-9) contains supplementary material, which is available to authorized users.

Therapies and outcomes of congenital hyperinsulinism-induced hypoglycaemia

Congenital hyperinsulinism is a rare disease, but is the most frequent cause of persistent and severe hypoglycaemia in early childhood. Hypoglycaemia caused by excessive and dysregulated insulin secretion (hyperinsulinism) from disordered pancreatic β cells can often lead to irreversible brain damage with lifelong neurodisability. Although congenital hyperinsulinism has a genetic cause in a significant proportion (40%) of children, often being the result of mutations in the genes encoding the K_ATP channel (ABCC8 and KCNJ11), not all children have severe and persistent forms of the disease. In approximately half of those without a genetic mutation, hyperinsulinism may resolve, although timescales are unpredictable. From a histopathology perspective, congenital hyperinsulinism is broadly grouped into diffuse and focal forms, with surgical lesionectomy being the preferred choice of treatment in the latter. In contrast, in diffuse congenital hyperinsulinism, medical treatment is the best option if conservative management is safe and effective. In such cases, children receiving treatment with drugs, such as diazoxide and octreotide, should be monitored for side effects and for signs of reduction in disease severity. If hypoglycaemia is not safely managed by medical therapy, subtotal pancreatectomy may be required; however, persistent hypoglycaemia may continue after surgery and diabetes is an inevitable consequence in later life. It is important to recognize the negative cognitive impact of early-life hypoglycaemia which affects half of all children with congenital hyperinsulinism. Treatment options should be individualized to the child/young person with congenital hyperinsulinism, with full discussion regarding efficacy, side effects, outcomes and later life impact.

Identification, pathophysiology, and clinical implications of primary insulin hypersecretion in nondiabetic adults and adolescents

BACKGROUND

Excessive insulin secretion may lead to glucose dysregulation. Our aim was to identify primary (independent of insulin resistance) insulin hypersecretion in subjects with normal glucose tolerance and its role in the progression of dysglycemia.

METHODS

In 1,168 adults, insulin secretion rate (ISR) and β cell function were estimated by C-peptide modeling during an oral glucose tolerance test (OGTT) and an i.v. glucose tolerance test. Whole-body insulin sensitivity was measured by a hyperinsulinemic-euglycemic clamp. After regressing ISR on insulin sensitivity, subjects in the upper tertile of the distribution of residuals were defined as primary hypersecretors. This approach was applied to a biethnic cohort of 182 obese adolescents, who received an OGTT, a hyperglycemic, and a euglycemic clamp.

RESULTS

Adult hypersecretors showed older age, more familial diabetes, sedentary lifestyle, increased fat mass, and worse lipid profile compared with the rest of the cohort, despite virtually identical BMI and insulin sensitivity. Insulin secretion was increased by 53% due to enhanced (+23%) β cell glucose sensitivity. Despite the resulting hyperinsulinemia, glucose tolerance was worse in hypersecretors among both adults and adolescents, coupled with higher indices of liver insulin resistance and increased availability of gluconeogenic substrates. At the 3-year follow-up, adult hypersecretors had increased incidence of impaired glucose tolerance/type 2 diabetes.

CONCLUSION

Primary insulin hypersecretion, independent of insulin resistance, is associated with a worse clinical and metabolic phenotype in adults and adolescents and predicts deterioration of glucose control over time.

FUNDING

The relationship between insulin sensitivity and cardiovascular disease (RISC) Study was partly supported by EU grant QLG1-CT-2001-01252.

Spacial models of malfunctioned protein complexes help to elucidate signal transduction critical for insulin release

Mutations in gene KCNJ11 encoding the Kir6.2 subunit of the ATP-sensitive potassium channel (KATP), a representative of a quite complex biosystem, may affect insulin release from pancreatic beta-cells. Both gain and loss of channel activity are observed, which lead to varied clinical phenotypes ranging from neonatal diabetes to congenital hyperinsulinism. In order to understand the mechanisms of the channel function better we mapped, based on the literature review, known medically relevant Kir6.2/SUR1 mutations into recently (2017) determined CryoEM 3D structures of this complex. We used a clustering algorithm to find hots spots in the 3D structure, thus we may hypothesize about their nano-mechanical role in the channel gating and the insulin level control. We also adapted a simple model of the channel gating to cover all currently known factors that can influence the KATP biosystem functions.

Diazoxide toxicity in a child with persistent hyperinsulinemic hypoglycemia of infancy: mixed hyperglycemic hyperosmolar coma and ketoacidosis

BACKGROUND

Persistent hyperinsulinemic hypoglycemia of infancy (PHHI), also known as congenital hyperinsulinism, has been known to go into spontaneous remission, with patients developing diabetes in later life. A temporary phase of hyperglycemia is, however, rarely reported.

CASE PRESENTATION

We describe a 16-month-old child, a known case of diazoxide responsive PHHI, presenting with mixed hyperglycemic hyperosmolar coma and ketoacidosis with rhabdomyolysis while on diazoxide treatment. The patient required temporary cessation of diazoxide and initiation of insulin infusion, followed by a relapse of hypoglycemia again necessitating diazoxide therapy.

CONCLUSIONS

Hyperosmolar coma with ketoacidosis is a rare side-effect of diazoxide therapy, documented even in patients with persistent hyperinsulinemic hypoglycemia of infancy.

Ablation of somatostatin cells leads to impaired pancreatic islet function and neonatal death in rodents

The somatostatin (SST)-secreting cells were mainly distributed in the pancreatic islets, brain, stomach and intestine in mammals and have many physiological functions. In particular, the SST-secreting δ cell is the third most common cell type in the islets of Langerhans. Recent studies have suggested that dysregulation of paracrine interaction between the pancreatic δ cells and β cells results in impaired glucose homeostasis and contributes to diabetes development. However, direct evidence of the functional importance of SST cells in glucose homeostasis control is still lacking. In the present study, we specifically ablated SST-secreting cells by crossing Sst-cre transgenic mice with R26 ^DTA mice (Sst ^Cre R26 ^DTA ). The Sst ^Cre R26 ^DTA mice exhibited neonatal death. The life spans of these mice with severe hypoglycemia were extended by glucose supplementation. Moreover, we observed that SST cells deficiency led to increased insulin content and excessive insulin release, which might contribute to the observed hypoglycemia. Unexpectedly, although SST is critical for the regulation of insulin content, factors other than SST that are produced by pancreatic δ cells via their endogenous corticotropin-releasing hormone receptor 2 (CRHR2) activity play the main roles in maintaining normal insulin release, as well as neonatal glucose homeostasis in the resting state. Taken together, our results identified that the SST cells in neonatal mouse played critical role in control of insulin release and normal islet function. Moreover, we provided direct in vivo evidence of the functional importance of the SST cells, which are essential for neonatal survival and the maintenance of glucose homeostasis.

Randomised controlled trial of diazoxide for small for gestational age neonates with hyperinsulinaemic hypoglycaemia provided early hypoglycaemic control without adverse effects

AIM

Hyperinsulinaemic hypoglycaemia (HH) is a very common cause of hypoglycaemia in small for gestational age (SGA) neonates. We compared using early oral diazoxide or a placebo for this patient group.

METHODS

This was a randomised, double-blind, placebo-controlled trial that focused on SGA neonates born at at least 32 weeks of gestation with HH during the first five days of life. Neonates with severe perinatal asphyxia, sepsis or contraindications for oral feeds were excluded. The primary outcome was the hours taken to achieve hypoglycaemic control, with a glucose infusion rate of ≤4 mg/kg/min. The secondary outcomes were the duration of intravenous fluids, sepsis episodes, time to achieve full feeds and mortality.

RESULTS

We screened 490 neonates and 30 neonates were eligible for randomisation and completed the trial. Half received diazoxide and half received a placebo. The median time to achieve hypoglycaemia control (40 vs 71.5 hours, p = 0.015), the total duration of intravenous fluids (114 vs 164 hours, p = 0.04) and time to achieve full feeds (74 vs 124 hours, p = 0.02) were significantly lower in the diazoxide group, with no adverse effects attributed to the drug.

CONCLUSION

Using oral diazoxide for SGA neonates with HH provided early hypoglycaemic control with no apparent adverse effects.

Association of maternal nutrition with transient neonatal hyperinsulinism

Objective

The objective was to determine whether maternal nutritional factors are associated with transient neonatal hyperinsulinism (HI).

Design and setting

Case control study in 4 French tertiary Obstetrics and Neonatology Departments between 2008 and 2015.

Methods

Sixty-seven mothers of neonates diagnosed with transient hyperinsulinism and 113 mothers of controls were included. The screening for hyperinsulinemic hypoglycemia in neonates was performed because of clinical symptoms suggestive of hypoglycemia or in the presence of conventional risk factors (small-for-gestational-age, prematurity, anoxo-ischemia, hypothermia, macrosomia, gestational diabetes). Hyperinsulinemic hypoglycemia was confirmed in the HI neonates and ruled out in the controls. This allowed for comparing maternal nutrition in cases and controls in a context of similar risk factors. One to 2 mothers of control neonates were included per case, and a food frequency questionnaire was addressed to the mothers between day 5 and day 10 after the birth of their newborn.

Results

Crude odds ratio showed that maternal weight gain, abnormal fetal rate, C-section, gender, consumption of fresh cooked vegetables, fresh fruits and fruit juices, low fat diary products, light fat products, and daily bread were significantly associated with hyperinsulinism. Maternal body mass index, hypertension, gestational diabetes, birth weight percentile, gestational age and 5-minute Apgar score were not related to HI. In a multiple backward logistic regression model, consumption of fresh cooked vegetable ≥1/day (OR = 0.33 [0.14–0.77]) and light-fat products ≥1/week (OR = 0.24 [0.08–0.71]) was protective against hyperinsulinism, whereas gestational weight gain >20 kg (OR = 9.5 [2.0–45.5]) and between 15–20 kg (OR = 4.0 [1.2–14.0]), abnormal fetal heart rate (OR = 4.4 [1.6–12.0]), and C-section (OR = 3.4 [1.3–8.9]) were risk factors.

Conclusions

A diet rich in fresh cooked vegetable and reduced in fat, together with the avoidance of a high gestational weight gain may be protective against transient neonatal hyperinsulinism.

Regulation of KATP Channel Trafficking in Pancreatic β-Cells by Protein Histidine Phosphorylation

Protein histidine phosphatase 1 (PHPT-1) is an evolutionarily conserved 14-kDa protein that dephosphorylates phosphohistidine. PHPT-1^-/- mice were generated to gain insight into the role of PHPT-1 and histidine phosphorylation/dephosphorylation in mammalian biology. PHPT-1^-/- mice exhibited neonatal hyperinsulinemic hypoglycemia due to impaired trafficking of K_ATP channels to the plasma membrane in pancreatic β-cells in response to low glucose and leptin and resembled patients with congenital hyperinsulinism (CHI). The defect in K_ATP channel trafficking in PHPT-1^-/- β-cells was due to the failure of PHPT-1 to directly activate transient receptor potential channel 4 (TRPC4), resulting in decreased Ca²⁺ influx and impaired downstream activation of AMPK. Thus, these studies demonstrate a critical role for PHPT-1 in normal pancreatic β-cell function and raise the possibility that mutations in PHPT-1 and/or TRPC4 may account for yet to be defined cases of CHI.

Benign Tumors and Tumorlike Lesions of the Pancreas

The pancreas is a complex organ that may give rise to large number of neoplasms and non-neoplastic lesions. This article focuses on benign neoplasms, such as serous neoplasms, and tumorlike (pseudotumoral) lesions that may be mistaken for neoplasm not only by clinicians and radiologists, but also by pathologists. The family of pancreatic pseudotumors, by a loosely defined conception of that term, includes a variety of lesions including heterotopia, hamartoma, and lipomatous pseudohypertrophy. Autoimmune pancreatitis and paraduodenal ("groove") pancreatitis may also lead to pseudotumor formation. Knowledge of these entities will help in making an accurate diagnosis.

Population pharmacokinetics of exendin-(9-39) and clinical dose selection in patients with congenital hyperinsulinism

AIMS

Congenital hyperinsulinism (HI) is the most common cause of persistent hypoglycaemia in infants and children. Exendin-(9-39), an inverse glucagon-like peptide 1 (GLP-1) agonist, is a novel therapeutic agent for HI that has demonstrated glucose-raising effect. We report the first population pharmacokinetic (PopPK) model of the exendin-(9-39) in patients with HI and propose the optimal dosing regimen for future clinical trials in neonates with HI.

METHODS

A total of 182 pharmacokinetic (PK) observations from 26 subjects in three clinical studies were included for constructing the PopPK model using first order conditional estimation (FOCE) with interaction method in nonlinear mixed-effects modelling (NONMEM). Exposure metrics (area under the curve [AUC] and maximum plasma concentration [C_max ]) at no observed adverse effect levels (NOAELs) in rats and dogs were determined in toxicology studies.

RESULTS

Observed concentration-time profiles of exendin-(9-39) were described by a linear two-compartmental PK model. Following allometric scaling of PK parameters, age and creatinine clearance did not significantly affect clearance. The calculated clearance and elimination half-life for adult subjects with median weight of 69 kg were 11.8 l h^-1 and 1.81 h, respectively. The maximum recommended starting dose determined from modelling and simulation based on the AUC_0-last at the NOAEL and predicted AUC_0-inf using the PopPK model was 27 mg kg^-1  day^-1 intravenously.

CONCLUSIONS

This is the first study to investigate the PopPK of exendin-(9-39) in humans. The final PopPK model was successfully used with preclinical toxicology findings to propose the optimal dosing regimen of exendin-(9-39) for clinical studies in neonates with HI, allowing for a more targeted dosing approach to achieve desired glycaemic response.

Congenital Hyperinsulinism: Diagnosis and Treatment Update

Pancreatic β-cells are finely tuned to secrete insulin so that plasma glucose levels are maintained within a narrow physiological range (3.5-5.5 mmol/L). Hyperinsulinaemic hypoglycaemia (HH) is the inappropriate secretion of insulin in the presence of low plasma glucose levels and leads to severe and persistent hypoglycaemia in neonates and children. Mutations in 12 different key genes (ABCC8, KCNJ11, GLUD1, GCK, HADH, SLC16A1, UCP2, HNF4A, HNF1A, HK1, PGM1 and PMM2) that are involved in the regulation of insulin secretion from pancreatic β-cells have been described to be responsible for the underlying molecular mechanisms leading to congenital HH. In HH due to the inhibitory effect of insulin on lipolysis and ketogenesis there is suppressed ketone body formation in the presence of hypoglycaemia thus leading to increased risk of hypoglycaemic brain injury. Therefore, a prompt diagnosis and immediate management of HH is essential to avoid hypoglycaemic brain injury and long-term neurological complications in children. Advances in molecular genetics, imaging techniques (18F-DOPA positron emission tomography/computed tomography scanning), medical therapy and surgical advances (laparoscopic and open pancreatectomy) have changed the management and improved the outcome of patients with HH. This review article provides an overview to the background, clinical presentation, diagnosis, molecular genetics and therapy in children with different forms of HH.

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

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

KATP Channel Mutations and Neonatal Diabetes

Since the discovery of the KATP channel in 1983, numerous studies have revealed its physiological functions. The KATP channel is expressed in various organs, including the pancreas, brain and skeletal muscles. It functions as a "metabolic sensor" that converts the metabolic status to electrical activity. In pancreatic beta-cells, the KATP channel regulates the secretion of insulin by sensing a change in the blood glucose level and thus maintains glucose homeostasis. In 2004, heterozygous gain-of-function mutations in the KCNJ11 gene, which encodes the Kir6.2 subunit of the KATP channel, were found to cause neonatal diabetes. In some mutations, diabetes is accompanied by severe neurological symptoms [developmental delay, epilepsy, neonatal diabetes (DEND) syndrome]. This review focuses on mutations of Kir6.2, the pore-forming subunit and sulfonylurea receptor (SUR) 1, the regulatory subunit of the KATP channel, which cause neonatal diabetes/DEND syndrome and also discusses the findings of the pathological mechanisms that are associated with neonatal diabetes, and its neurological features.

"Riding High on Low Fuel" - Our Experience with Endogenous Hyperinsulinemic Hypoglycemia

INTRODUCTION

Endogenous hyperinsulinemic hypoglycemia (EHH) is a condition in which the insulin levels are inappropriately high in the presence of low plasma glucose.

MATERIALS AND METHODS

We did a retrospective analysis of case records of those patients admitted and evaluated for EHH from June 2004 to June 2016 in our center, excluding those that were diagnosed with reactive hypoglycemia. We collected data regarding demographics, clinical presentation, laboratory results, localization techniques, and treatment administered.

RESULTS

Sixteen patients who were admitted for evaluation based on history suggestive of repeated hypoglycemic episodes were included in the study. All but one pregnant patient was subjected to a supervised fast in the hospital. All patients developed hypoglycemia (defined using Whipple's triad) within the first 24 h. Three patients had autoimmune hypoglycemia which differed significantly from insulinoma-mediated hypoglycemia in certain clinical and laboratory parameters. They were older in age with marked fluctuations in the 24 h glucose profile ranging from frank hypoglycemia to frank hyperglycemia. The insulin levels were markedly elevated in this group of patients along with a significantly elevated insulin C peptide molar ratio (ICMR) when compared with patients with insulinoma-mediated hypoglycemia.

CONCLUSIONS

Although insulinoma is the most common cause of EHH, autoimmune hypoglycemia should be considered as a differential diagnosis, particularly in older individuals with plasma glucose values increasing to the hyperglycemic range. Degree of elevation of insulin levels and ICMR may provide additional clues. Overall, the survival and prognosis of patients with EHH are excellent.

Diagnosis and treatment of hyperinsulinaemic hypoglycaemia and its implications for paediatric endocrinology

Glucose homeostasis requires appropriate and synchronous coordination of metabolic events and hormonal activities to keep plasma glucose concentrations in a narrow range of 3.5–5.5 mmol/L. Insulin, the only glucose lowering hormone secreted from pancreatic β-cells, plays the key role in glucose homeostasis. Insulin release from pancreatic β-cells is mainly regulated by intracellular ATP-generating metabolic pathways. Hyperinsulinaemic hypoglycaemia (HH), the most common cause of severe and persistent hypoglycaemia in neonates and children, is the inappropriate secretion of insulin which occurs despite low plasma glucose levels leading to severe and persistent hypoketotic hypoglycaemia. Mutations in 12 different key genes (ABCC8, KCNJ11, GLUD1, GCK, HADH, SLC16A1, UCP2, HNF4A, HNF1A, HK1, PGM1 and PMM2) constitute the underlying molecular mechanisms of congenital HH. Since insulin supressess ketogenesis, the alternative energy source to the brain, a prompt diagnosis and immediate management of HH is essential to avoid irreversible hypoglycaemic brain damage in children. Advances in molecular genetics, imaging methods (¹⁸F–DOPA PET-CT), medical therapy and surgical approach (laparoscopic and open pancreatectomy) have changed the management and improved the outcome of patients with HH. This up to date review article provides a background to the diagnosis, molecular genetics, recent advances and therapeutic options in the field of HH in children.

Hyperinsulinemic hypoglycemia: clinical, molecular and therapeutical novelties

Hyperinsulinemic hypoglycemia (HI) is the most common cause of hypoglycemia in children. Impairment of cellular pathways involved in insulin secretion from pancreatic β-cells, broadly classified as channelopathies and metabolopathies, have been discovered in the past two decades. The increasing use of NGS target panels, combined with clinical, biochemical and imaging findings allows differentiating the diagnostic management of children with focal forms, surgically curable, from those with diffuse forms, more conservatively treated with pharmacological and nutritional interventions. Specific approaches according to the subtype of HI have been established and novel therapies are currently under investigation. Despite diagnostic and therapeutic advances, HI remains an important cause of morbidity in children, still accounting for 26-44% of permanent intellectual disabilities, especially in neonatal-onset patients. Initial insult from recurrent hypoglycemia in early life greatly contributes to the poor outcomes. Therefore, patients need to be rapidly identified and treated aggressively, and require at follow-up a complex and regular monitoring, managed by a multidisciplinary HI team. This review gives an overview on the more recent diagnostic and therapeutic tools, on the novel drug and nutritional therapies, and on the long-term neurological outcomes.

Hyperinsulinism-Causing Mutations Cause Multiple Molecular Defects in SUR1 NBD1

The sulfonylurea receptor 1 (SUR1) protein forms the regulatory subunit in ATP sensitive K⁺ (K_ATP) channels in the pancreas. SUR proteins are members of the ATP binding cassette (ABC) superfamily of proteins. Binding and hydrolysis of MgATP at the SUR nucleotide binding domains (NBDs) lead to channel opening. Pancreatic K_ATP channels play an important role in insulin secretion. SUR1 mutations that result in increased levels of channel opening ultimately inhibit insulin secretion and lead to neonatal diabetes. In contrast, SUR1 mutations that disrupt trafficking and/or decrease gating of K_ATP channels cause congenital hyperinsulinism, where oversecretion of insulin occurs even in the presence of low glucose levels. Here, we present data on the effects of specific congenital hyperinsulinism-causing mutations (G716V, R842G, and K890T) located in different regions of the first nucleotide binding domain (NBD1). Nuclear magnetic resonance (NMR) and fluorescence data indicate that the K890T mutation affects residues throughout NBD1, including residues that bind MgATP, NBD2, and coupling helices. The mutations also decrease the MgATP binding affinity of NBD1. Size exclusion and NMR data indicate that the G716V and R842G mutations cause aggregation of NBD1 in vitro, possibly because of destabilization of the domain. These data describe structural characterization of SUR1 NBD1 and shed light on the underlying molecular basis of mutations that cause congenital hyperinsulinism.

A Novel Homozygous Mutation in the KCNJ11 Gene of a Neonate with Congenital Hyperinsulinism and Successful Management with Sirolimus

Congenital hyperinsulinism (CHI) is the most common cause of neonatal persistent hypoglycemia caused by mutations in nine known genes. Early diagnosis and treatment are important to prevent brain injury. The clinical presentation and response to pharmacological therapy may vary depending on the underlying pathology. Genetic analysis is important in the diagnosis, treatment, patient follow-up, and prediction of recurrence risk within families. Our patient had severe hypoglycemia and seizure following birth. His diagnostic evaluations including genetic testing confirmed CHI. He was treated with a high-glucose infusion, high-dose diazoxide, nifedipine, and glucagon infusion. A novel homozygous mutation (p.F315I) in the KCNJ11 gene, leading to diazoxide-unresponsive CHI, was identified. Both parents were heterozygous for this mutation. Our patient's clinical course was complicated by severe refractory hypoglycemia; he was successfully managed with sirolimus and surgical intervention was not required. Diazoxide, nifedipine, and glucagon were discontinued gradually following sirolimus therapy. The patient was discharged at 2 months of age on low-dose octreotide and sirolimus. His outpatient clinical follow-up continues with no episodes of hypoglycemia. We present a novel homozygous p.F315I mutation in the KCNJ11 gene leading to diazoxide-unresponsive CHI in a neonate. This case illustrates the challenges associated with the diagnosis and management of CHI, as well as the successful therapy with sirolimus.

The ATP-sensitive K channel is seizure protective and required for effective dietary therapy in a model of mitochondrial encephalomyopathy

Effective therapies are lacking for mitochondrial encephalomyopathies (MEs). MEs are devastating diseases that predominantly affect the energy-demanding tissues of the nervous system and muscle, causing symptoms such as seizures, cardiomyopathy, and neuro- and muscular degeneration. Even common anti-epileptic drugs which are frequently successful in ameliorating seizures in other diseases tend to have a lower success rate in ME, highlighting the need for novel drug targets, especially those that may couple metabolic sensitivity to neuronal excitability. Furthermore, alternative epilepsy therapies such as dietary modification are gaining in clinical popularity but have not been thoroughly studied in ME. Using the Drosophila ATP6¹ model of ME, we have studied dietary therapy throughout disease progression and found that it is highly effective against the seizures of ME, especially a high fat/ketogenic diet, and that the benefits are dependent upon a functional K_ATP channel complex. Further experiments with K_ATP show that it is seizure-protective in this model, and that pharmacological promotion of its open state also ameliorates seizures. These studies represent important steps forward in the development of novel therapies for a class of diseases that is notoriously difficult to treat, and lay the foundation for mechanistic studies of currently existing therapies in the context of metabolic disease.

Dynamics and Regulation of Insulin Secretion in Pancreatic Islets from Normal Young Children

Insulin secretion has only exceptionally been investigated in pancreatic islets from healthy young children. It remains unclear whether those islets behave like adult islets despite substantial differences in cellular composition and higher β-cell replication rates. Islets were isolated from 5 infants/toddlers (11–36 month-old) and perifused to characterize their dynamics of insulin secretion when subjected to various stimuli and inhibitors. Their insulin responses were compared to those previously reported for similarly treated adult islets. Qualitatively, infant islets responded like adult islets to stimulation by glucose, tolbutamide, forskolin (to increase cAMP), arginine and the combination of leucine and glutamine, and to inhibition by diazoxide and CaCl₂ omission. This similarity included the concentration-dependency and biphasic pattern of glucose-induced insulin secretion, the dynamics of the responses to non-glucose stimuli and metabolic amplification of these responses. The insulin content was not different, but fractional insulin secretion rates were lower in infant than adult islets irrespective of the stimulus. However, the stimulation index was similar because basal secretion rates were also lower in infant islets. In conclusion, human β-cells are functionally mature by the age of one year, before expansion of their mass is complete. Their responsiveness (stimulation index) to all stimuli is not smaller than that of adult β-cells. Yet, under basal and stimulated conditions, they secrete smaller proportions of their insulin stores in keeping with smaller in vivo insulin needs during infancy.

Single incision laparoscopic 90 % pancreatectomy for the treatment of persistent hyperinsulinemic hypoglycemia of infancy

Single incision laparoscopic surgery as a surgical approach in treatment of pancreatic disease has recently been reported in adults. However, its application in persistent hyperinsulinemic hypoglycemia of infancy (PHHI) in children is limited. In this article, we report single incision laparoscopic 90 % pancreatectomy for the treatment of persistent hyperinsulinemic hypoglycemia of infancy. Between July 2011 and February 2015, the single incision laparoscopic 90 % pancreatectomy was performed in three children with PHHI. All patients underwent (18)F-FDOPA PET/CT before the surgeries. The scans showed diffuse physiologic (18)F-FDOPA activity in entire pancreas. All patients were followed up. The levels of blood sugar and insulin were recorded postoperatively. The time required for surgery was 120-230 min, and blood loss was minimal. The hospital stay was 6 days. The duration of postoperative abdominal drainage was 4-5 days. The levels of fasting blood glucose after surgery were higher than those before surgery (4.38-8.9 vs. 0.54-1.8 mmol/L). The levels of fasting insulin after surgery were lower than those before surgery (2.4-5.5 vs. 14-33.3 uU/ml). The duration of follow-up was 4-46 months. During follow-up, the levels of blood glucose and insulin were normal in three patients. There was no recurrence of hypoglycemia after operation in all patients. Single incision laparoscopic 90 % pancreatectomy for children with PHHI is feasible and safe in well-selected cases in the experienced centers.

Genetic characteristics and long-term follow-up of 11 patients with congenital hyperinsulinism followed in a single center

BACKGROUND

Congenital hyperinsulinism (CHI) is a rare disease with an estimated incidence of 1:40,000 live births. Here, we characterize 11 patients treated at Munich Children's Hospital Schwabing.

METHODS

We analyzed data on birth, treatment and laboratory results including genetic testing and evaluated the long-term course with a follow-up visit.

RESULTS

All patients had severe, diazoxide-(DZX)-resistant hypoglycemia, beginning immediately after birth. Two patients were treated by medical therapy, eight underwent subtotal pancreatectomy and one had a partial resection. Both patients who had medical therapy still suffer from occasional hypoglycemia. Six patients with subtotal pancreatectomy were affected by mild hypoglycemia. Seventy-five percent of patients who had surgical treatment developed diabetes mellitus (DM) at a median age of 10.5 (8-13) years. In 89% of patients with available genetic testing, mutations of the ABCC8 gene were detected.

CONCLUSIONS

The majority of CHI-patients not responding to DZX underwent surgery. After subtotal pancreatectomy, patients typically developed diabetes around early puberty.

Genome-edited human stem cell-derived beta cells: a powerful tool for drilling down on type 2 diabetes GWAS biology

Type 2 diabetes (T2D) is a disease of pandemic proportions, one defined by a complex aetiological mix of genetic, epigenetic, environmental, and lifestyle risk factors. Whilst the last decade of T2D genetic research has identified more than 100 loci showing strong statistical association with disease susceptibility, our inability to capitalise upon these signals reflects, in part, a lack of appropriate human cell models for study. This review discusses the impact of two complementary, state-of-the-art technologies on T2D genetic research: the generation of stem cell-derived, endocrine pancreas-lineage cells and the editing of their genomes. Such models facilitate investigation of diabetes-associated genomic perturbations in a physiologically representative cell context and allow the role of both developmental and adult islet dysfunction in T2D pathogenesis to be investigated. Accordingly, we interrogate the role that patient-derived induced pluripotent stem cell models are playing in understanding cellular dysfunction in monogenic diabetes, and how site-specific nucleases such as the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system are helping to confirm genes crucial to human endocrine pancreas development. We also highlight the novel biology gleaned in the absence of patient lines, including an ability to model the whole phenotypic spectrum of diabetes phenotypes occurring both in utero and in adult cells, interrogating the non-coding 'islet regulome' for disease-causing perturbations, and understanding the role of other islet cell types in aberrant glycaemia. This article aims to reinforce the importance of investigating T2D signals in cell models reflecting appropriate species, genomic context, developmental time point, and tissue type.

Enhanced Islet Cell Nucleomegaly Defines Diffuse Congenital Hyperinsulinism in Infancy but Not Other Forms of the Disease

OBJECTIVES

To quantify islet cell nucleomegaly in controls and tissues obtained from patients with congenital hyperinsulinism in infancy (CHI) and to examine the association of nucleomegaly with proliferation.

METHODS

High-content analysis of histologic sections and serial block-face scanning electron microscopy were used to quantify nucleomegaly.

RESULTS

Enlarged islet cell nuclear areas were 4.3-fold larger than unaffected nuclei, and the mean nuclear volume increased to approximately threefold. Nucleomegaly was a normal feature of pediatric islets and detected in the normal regions of the pancreas from patients with focal CHI. The incidence of nucleomegaly was highest in diffuse CHI (CHI-D), with more than 45% of islets containing two or more affected cells. While in CHI-D nucleomegaly was negatively correlated with cell proliferation, in all other cases, there was a positive correlation.

CONCLUSIONS

Increased incidence of nucleomegaly is pathognomonic for CHI-D, but these cells are nonproliferative, suggesting a novel role in the pathobiology of this condition.