Diabetes and insulin secretion: the ATP-sensitive K+ channel (K ATP) connection

The impact of GLP-1 signalling on the energy metabolism of pancreatic islet β-cells and extrapancreatic tissues

Glucagon-like peptide-1 signalling impacts glucose homeostasis and appetite thereby indirectly affecting substrate availability at the whole-body level. The incretin canonically produces an insulinotropic effect, thereby lowering blood glucose levels by promoting the uptake and inhibiting the production of the sugar by peripheral tissues. Likewise, GLP-1 signalling within the central nervous system reduces the appetite and food intake, whereas its gastric effect delays the absorption of nutrients, thus improving glycaemic control and reducing the risk of postprandial hyperglycaemia. We review the molecular aspects of the GLP-1 signalling, focusing on its impact on intracellular energy metabolism. Whilst the incretin exerts its effects predominantly via a Gs receptor, which decodes the incretin signal into the elevation of intracellular cAMP levels, the downstream signalling cascades within the cell, acting on fast and slow timescales, resulting in an enhancement or an attenuation of glucose catabolism, respectively.

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.

HCV affects KATP channels through GnT-IVa-mediated N-glycosylation of GLUT2 on the surface of pancreatic β-cells leading to impaired insulin secretion

PURPOSE

To explore the mechanism of insulin secretion dysfunction in pancreatic beta cells induced by N-glycosylation mediated by an infection from the hepatitis C virus (HCV).

METHODS

Min6 cell models infected with HCV and stimulated with glucose were constructed. Meanwhile, an HCV-infected animal model and a type 2 diabetes mellitus (T2DM) rat model were constructed. Glucose uptake in the Min6 cells was detected, and insulin secretion was detected by ELISA. Flow cytometry, immunofluorescence staining, Western blotting, RT-qPCR, and lectin blotting were used to detect the expression levels of related proteins and mRNA, as well as the level of N-glycosylation. HE staining was used to observe the pathological changes in the pancreatic tissue, and an oral glucose tolerance test (OGTT) was used to evaluate the glucose tolerance of the rats.

RESULTS

Compared with the NC group, the expression levels of GnT-IVa, GLUT2, galectin-9, and voltage-dependent calcium channel 1.2 (Cav1.2) were significantly downregulated in the HCV-infected group. The ATP-sensitive potassium channel (KATP) component proteins SUR1 and Kir6.2 were significantly upregulated, while intracellular glucose intake and insulin secretion decreased, N-glycosylation levels and ATP levels significantly decreased, and the overexpression of GnT-IVa reversed the effect of the HCV infection. However, treatment with the glycosylation inhibitor kifunensine (KIF) or the KATP channel activator diazine (Dia) reversed the effects of the overexpression of GnT-IVa. In the animal experiments, HE staining revealed serious pathological injuries in the pancreatic tissue of the HCV-infected rats, with decreased glucose tolerance and glycosylation levels, decreased insulin secretion, downregulated expression of GnT-IVa, GLUT2, and Cav1.2, and upregulated expression of SUR1 and Kir6.2. The overexpression treatment of GnT-IVa or the KATP channel antagonist miglinide reversed the effects of HCV.

CONCLUSION

HCV infection inhibits GLUT2 N-glycosylation on the pancreatic β cell surface by downregulating the expression of GnT-IVa and then activates the KATP pathway, which ultimately leads to disturbances in insulin secretion.

A Woman With HNF1A-Associated Monogenic Diabetes Treated Successfully With Repaglinide Monotherapy

Background/Objective

Monogenic diabetes is a rare type of diabetes that is commonly misdiagnosed as type 1 or 2 diabetes mellitus, which adversely impacts patient care. Such cases are particularly challenging given the heterogeneity in presentation and overlap with other types of diabetes. As the sole use of meglitinides, especially repaglinide, to treat HNF1A-associated monogenic diabetes has been rarely reported in a few other observational studies, we describe a patient who was treated successfully with repaglinide.

Case Report

A 38-year-old woman with type 1 diabetes mellitus, congenital deafness, chronic kidney disease, and retinopathy presented with difficulty controlling her blood glucose levels. Although initially treated with insulin, she had periods of noncompliance with insulin without experiencing diabetic ketoacidosis. Although on insulin therapy, she experienced multiple episodes of hypoglycemia. The laboratory tests showed a hemoglobin A1c level of 10.8%, c-peptide level of 2.7 ng/mL (1.1-4.4 ng/mL), glucose level of 192 mg/dL, creatinine level of 1.23 ng/dL, and severely increased microalbumin-to-creatinine ratio of 638 mg/g (normal range, 0-29 mg/g). Pancreatic autoantibodies were negative. Genetic testing revealed a diagnosis of HNF1A-associated monogenic diabetes (c. 1340C>T (p.P447L)). She was ultimately treated with repaglinide after trials of sulfonylureas and dipeptidyl peptidase 4 inhibitors led to frequent hypoglycemia and a significant increase in the hemoglobin A1c level, respectively.

Discussion

This case highlights the importance of correctly diagnosing monogenic diabetes and reports the successful use of repaglinide to treat HNF1A-associated monogenic diabetes.

Conclusion

Patients with HNF1A-associated monogenic diabetes who do not achieve euglycemia with sulfonylureas and insulin may be successfully treated with repaglinide monotherapy.

The Perfect Cup? Coffee-Derived Polyphenols and Their Roles in Mitigating Factors Affecting Type 2 Diabetes Pathogenesis

Type 2 diabetes (T2D) is a growing health concern with an estimated 462 million people having been diagnosed worldwide. T2D is characterized by chronically elevated blood glucose and insulin resistance, which culminate in a diminished function of the β-cell mass in its later stages. This can be perpetuated by and result in inflammation, excess reactive oxygen species production, obesity, and the dysregulation of multiple cellular pathways. Many naturally occurring small molecules have been investigated in terms of their roles in modulating glucose homeostasis and β-cell function. Many of these compounds can be found in commonly used sources of food and drink. Interestingly, a correlation has been observed between coffee consumption and T2D incidence. However, the specific compounds responsible for this correlation and their mechanisms are still somewhat undetermined. This paper reviews recent research findings on the effects of several polyphenols that are either found in coffee or are metabolites of compounds found in coffee (enterodiol, enterolactone, matairesinol, secoisolariciresinol, kaempferol, quercetin, and chlorogenic acid) on glucose homeostasis and health complications associated with glucose dysregulation, with a special emphasis on their potential anti-diabetic effects. The factors that affect polyphenol content in coffee are also addressed.

Snake Venom: A Promising Source of Neurotoxins Targeting Voltage-Gated Potassium Channels

The venom derived from various sources of snakes represents a vast collection of predominantly protein-based toxins that exhibit a wide range of biological actions, including but not limited to inflammation, pain, cytotoxicity, cardiotoxicity, and neurotoxicity. The venom of a particular snake species is composed of several toxins, while the venoms of around 600 venomous snake species collectively encompass a substantial reservoir of pharmacologically intriguing compounds. Despite extensive research efforts, a significant portion of snake venoms remains uncharacterized. Recent findings have demonstrated the potential application of neurotoxins derived from snake venom in selectively targeting voltage-gated potassium channels (Kv). These neurotoxins include BPTI-Kunitz polypeptides, PLA2 neurotoxins, CRISPs, SVSPs, and various others. This study provides a comprehensive analysis of the existing literature on the significance of Kv channels in various tissues, highlighting their crucial role as proteins susceptible to modulation by diverse snake venoms. These toxins have demonstrated potential as valuable pharmacological resources and research tools for investigating the structural and functional characteristics of Kv channels.

Hypersensitivity to opening of ATP-sensitive potassium channels in post-traumatic headache

OBJECTIVE

To investigate whether levcromakalim (a KATP channel opener) induces migraine-like headache in people with persistent post-traumatic headache who had no known history of migraine.

METHODS

In a randomized, double-blind, placebo-controlled, 2-way crossover trial, participants were randomly assigned to receive a 20-minute continuous intravenous infusion of levcromakalim (50 µg/mL) or placebo (isotonic saline) on two separate experimental days with a 1-week wash-out period in between. The primary endpoint was the difference in incidence of migraine-like headache between levcromakalim and placebo during a 12-hour observational period after infusion start. The secondary endpoint was the difference in area under the curve for baseline-corrected median headache intensity scores between levcromakalim and placebo during the 12-hour observational period.

RESULTS

A total of 21 participants with persistent post-traumatic headache were randomized and completed the trial. During the 12-hour observational period, 12 (57%) of 21 participants reported experiencing migraine-like headache following the levcromakalim infusion, compared with three after placebo (P = 0.013). Moreover, the baseline-corrected median headache intensity scores were higher following the levcromakalim infusion than after placebo (P = 0.003).

CONCLUSION

Our findings suggest that KATP channels play an important role in the pathogenesis of migraine-like headache in people with persistent post-traumatic headache. This implies that KATP channel blockers might represent a promising avenue for drug development. Further research is warranted to explore the potential therapeutic benefits of KATP channel blockers in managing post-traumatic headache.Trial Registration: ClinicalTrials.gov Identifier: NCT05243953.

Pleiotrophin and metabolic disorders: insights into its role in metabolism

Pleiotrophin (PTN) is a cytokine which has been for long studied at the level of the central nervous system, however few studies focus on its role in the peripheral organs. The main aim of this review is to summarize the state of the art of what is known up to date about pleiotrophin and its implications in the main metabolic organs. In summary, pleiotrophin promotes the proliferation of preadipocytes, pancreatic β cells, as well as cells during the mammary gland development. Moreover, this cytokine is important for the structural integrity of the liver and the neuromuscular junction in the skeletal muscle. From a metabolic point of view, pleiotrophin plays a key role in the maintenance of glucose and lipid as well as whole-body insulin homeostasis and favors oxidative metabolism in the skeletal muscle. All in all, this review proposes pleiotrophin as a druggable target to prevent from the development of insulin-resistance-related pathologies.

Nutrigenomics of inward rectifier potassium channels

Inwardly rectifying potassium (Kir) channels play a key role in maintaining the resting membrane potential and supporting potassium homeostasis. There are many variants of Kir channels, which are usually tetramers in which the main subunit has two trans-membrane helices attached to two N- and C-terminal cytoplasmic tails with a pore-forming loop in between that contains the selectivity filter. These channels have domains that are strongly modulated by molecules present in nutrients found in different diets, such as phosphoinositols, polyamines and Mg²⁺. These molecules can impact these channels directly or indirectly, either allosterically by modulation of enzymes or via the regulation of channel expression. A particular type of these channels is coupled to cell metabolism and inhibited by ATP (KATP channels, essential for insulin release and for the pathogenesis of metabolic diseases like diabetes mellitus). Genomic changes in Kir channels have a significant impact on metabolism, such as conditioning the nutrients and electrolytes that an individual can take. Thus, the nutrigenomics of ion channels is an important emerging field in which we are attempting to understand how nutrients and diets can affect the activity and expression of ion channels and how genomic changes in such channels may be the basis for pathological conditions that limit nutrition and electrolyte intake. In this contribution we briefly review Kir channels, discuss their nutrigenomics, characterize how different components in the diet affect their function and expression, and suggest how their genomic changes lead to pathological phenotypes that affect diet and electrolyte intake.

The circadian rhythm: an influential soundtrack in the diabetes story

Type 2 Diabetes Mellitus (T2DM) has been the main category of metabolic diseases in recent years due to changes in lifestyle and environmental conditions such as diet and physical activity. On the other hand, the circadian rhythm is one of the most significant biological pathways in humans and other mammals, which is affected by light, sleep, and human activity. However, this cycle is controlled via complicated cellular pathways with feedback loops. It is widely known that changes in the circadian rhythm can alter some metabolic pathways of body cells and could affect the treatment process, particularly for metabolic diseases like T2DM. The aim of this study is to explore the importance of the circadian rhythm in the occurrence of T2DM via reviewing the metabolic pathways involved, their relationship with the circadian rhythm from two perspectives, lifestyle and molecular pathways, and their effect on T2DM pathophysiology. These impacts have been demonstrated in a variety of studies and led to the development of approaches such as time-restricted feeding, chronotherapy (time-specific therapies), and circadian molecule stabilizers.

Ca2+ release or Ca2+ entry, that is the question: what governs Ca2+ oscillations in pancreatic β cells?

The standard model for Ca2+ oscillations in insulin-secreting pancreatic β cells centers on Ca2+ entry through voltage-activated Ca2+ channels. These work in combination with ATP-dependent K+ channels, which are the bridge between the metabolic state of the cells and plasma membrane potential. This partnership underlies the ability of the β cells to secrete insulin appropriately on a minute-to-minute time scale to control whole body plasma glucose. Though this model, developed over more than 40 years through many cycles of experimentation and mathematical modeling, has been very successful, it has been challenged by a hypothesis that calcium-induced calcium release from the endoplasmic reticulum through ryanodine or inositol trisphosphate (IP3) receptors is instead the key driver of islet oscillations. We show here that the alternative model is in fact incompatible with a large body of established experimental data and that the new observations offered in support of it can be better explained by the standard model.

KATP channels are necessary for glucose-dependent increases in amyloid-β and Alzheimer's disease-related pathology

Elevated blood glucose levels, or hyperglycemia, can increase brain excitability and amyloid-β (Aβ) release, offering a mechanistic link between type 2 diabetes and Alzheimer's disease (AD). Since the cellular mechanisms governing this relationship are poorly understood, we explored whether ATP-sensitive potassium (KATP) channels, which couple changes in energy availability with cellular excitability, play a role in AD pathogenesis. First, we demonstrate that KATP channel subunits Kir6.2/KCNJ11 and SUR1/ABCC8 were expressed on excitatory and inhibitory neurons in the human brain, and cortical expression of KCNJ11 and ABCC8 changed with AD pathology in humans and mice. Next, we explored whether eliminating neuronal KATP channel activity uncoupled the relationship between metabolism, excitability, and Aβ pathology in a potentially novel mouse model of cerebral amyloidosis and neuronal KATP channel ablation (i.e., amyloid precursor protein [APP]/PS1 Kir6.2-/- mouse). Using both acute and chronic paradigms, we demonstrate that Kir6.2-KATP channels are metabolic sensors that regulate hyperglycemia-dependent increases in interstitial fluid levels of Aβ, amyloidogenic processing of APP, and amyloid plaque formation, which may be dependent on lactate release. These studies identify a potentially new role for Kir6.2-KATP channels in AD and suggest that pharmacological manipulation of Kir6.2-KATP channels holds therapeutic promise in reducing Aβ pathology in patients with diabetes or prediabetes.

Higher dietary magnesium and potassium intake are associated with lower body fat in people with impaired glucose tolerance

Introduction

Obesity and diabetes are public health concerns worldwide, but few studies have examined the habitual intake of minerals on body composition in people with prediabetes.

Methods

In this prospective cross-sectional study, 155 Chinese subjects with IGT [median age: 59 (53-62) years, 58% female] had an assessment of body composition including body fat percentage, oral glucose tolerance tests (OGTT), Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and 3-day food records from nutritional programme analysis.

Results

Dietary intake of minerals was negatively correlated with body fat. People with obesity had the lowest daily consumption of iron median (IQR) 10.3 (6.9-13.3) mg, magnesium 224 (181-282) mg, and potassium 1973 (1563-2,357) mg when compared to overweight [10.5 (8.0-14.5) mg, 273 (221-335) mg, and 2,204 (1720-2,650) mg] and normal weight individuals [13.2 (10.0-18.6) mg, 313 (243-368) mg, and 2,295 (1833-3,037) mg] (p = 0.008, <0.0001, and 0.013 respectively). Amongst targeted minerals, higher dietary magnesium and potassium intake remained significantly associated with lower body fat after the adjustment of age, gender, macronutrients, fibre, and physical activity.

Conclusion

Dietary magnesium and potassium intake may be associated with lower body fat in people with impaired glucose tolerance. Inadequate dietary mineral intake may play contribute to obesity and metabolic disorders independent of macronutrients and fibre consumption.

The ATP-dependent Pathways and Human Diseases

Adenosine triphosphate (ATP) is one of the most important molecules of life, present both inside the cells and extracellularly. It is an essential building block for nucleic acids biosynthesis and crucial intracellular energy storage. However, one of the most interesting functions of ATP is the role of a signaling molecule. Numerous studies indicate the involvement of ATP-dependent pathways in maintaining the proper functioning of individual tissues and organs. Herein, the latest data indicating the ATP function in the network of intra- and extracellular signaling pathways including purinergic signaling, MAP kinase pathway, mTOR and calcium signaling are collected. The main ATP-dependent processes maintaining the proper functioning of the nervous, cardiovascular and immune systems, as well as skin and bones, are summarized. The disturbances in the ATP amount, its cellular localization, or interaction with target elements may induce pathological changes in signaling pathways leading to the development of serious diseases. The impact of an ATP imbalance on the development of dangerous health dysfunctions such as neurodegeneration diseases, cardiovascular diseases (CVDs), diabetes mellitus, obesity, cancers and immune pathogenesis are discussed here.

Genome-edited zebrafish model of ABCC8 loss-of-function disease

ATP-sensitive potassium channel (KATP)gain- (GOF) and loss-of-function (LOF) mutations underlie human neonatal diabetes mellitus (NDM) and hyperinsulinism (HI), respectively. While transgenic mice expressing incomplete KATP LOF do reiterate mild hyperinsulinism, KATP knockout animals do not exhibit persistent hyperinsulinism. We have shown that islet excitability and glucose homeostasis are regulated by identical KATP channels in zebrafish. SUR1 truncation mutation (K499X) was introduced into the abcc8 gene to explore the possibility of using zebrafish for modeling human HI. Patch-clamp analysis confirmed the complete absence of channel activity in β-cells from K499X (SUR1-/-) fish. No difference in random blood glucose was detected in heterozygous SUR1+/- fish nor in homozygous SUR1-/- fish, mimicking findings in SUR1 knockout mice. Mutant fish did, however, demonstrate impaired glucose tolerance, similar to partial LOF mouse models. In paralleling features of mammalian diabetes and hyperinsulinism resulting from equivalent LOF mutations, these gene-edited animals provide valid zebrafish models of KATP -dependent pancreatic diseases.

Similarities in Calcium Oscillations Between Neonatal Mouse Islets and Mature Islets Exposed to Chronic Hyperglycemia

Pulsatility is important to islet function. As islets mature into fully developed insulin-secreting micro-organs, their ability to produce oscillatory intracellular calcium ([Ca2+]i) patterns in response to glucose also matures. In this study, we measured [Ca2+]i using fluorescence imaging to characterize oscillations from neonatal mice on postnatal (PN) days 0, 4, and 12 in comparison to adult islets. Under substimulatory (3-mM) glucose levels, [Ca2+]i was low and quiescent for adult islets as expected, as well as for PN day 12 islets. In contrast, one-third of islets on PN day 0 and 4 displayed robust [Ca2+]i oscillations in low glucose. In stimulatory glucose (11 mM) conditions, oscillations were present on all neonatal days but differed from patterns in adults. By PN day 12, [Ca2+]i oscillations were approaching characteristics of fully developed islets. The immature response pattern of neonatal islets was due, at least in part, to differences in adenosine 5'-triphosphate (ATP)-sensitive K+-channel activity estimated by [Ca2+]i responses to KATP channel agents diazoxide and tolbutamide. Neonatal [Ca2+]i patterns were also strikingly similar to patterns observed in mature islets exposed to hyperglycemic conditions (20 mM glucose for 48 hours): elevated [Ca2+]i and oscillations in low glucose along with reduced pulse mass in high glucose. Since a hallmark of diabetic islets is dedifferentiation, we propose that diabetic islets display features of "reverse maturation," demonstrating similar [Ca2+]i dynamics as neonatal islets. Pulsatility is thus an important emergent feature of neonatal islets. Our findings may provide insight into reversing β-cell dedifferentiation and to producing better functioning β cells from pluripotent stem cells.

Pharmacological Dose-Effect Profiles of Various Concentrations of Humanised Primary Bile Acid in Encapsulated Cells

Bile acids (BA)s are known surfactants and well-documented to play a major role in food digestion and absorption. Recently, potential endocrinological and formulation-stabilisation effects of BAs have been explored and their pharmacological effects on supporting cell survival and functions have gained wide interest. Hence, this study aimed to explore the hyper-glycaemic dependent dose-effect of the BA chenodeoxycholic acid (CDCA) when encapsulated with pancreatic β-cells, allowing assessment of CDCA's impacts when encapsulated. Four different concentrations of the BA were prepared, and viable cells were encapsulated and incubated for 2 days. Multiple analyses were carried out including confocal imaging, glucose-induced cellular mitochondrial viability indices, insulin production, inflammatory biomarker analyses and cellular bioenergetics measurements. There was a significant dose-effect with different concentrations of the BA, affecting cellular viability and antioxidant activities, cell functions and insulin release, inflammatory biomarkers, and cellular-bioenergetics at different oxidative stress levels. The results demonstrate that, when encapsulated, the BA CDCA exerts positive pharmacological effects at the cellular level, and such effects are concentration dependent.

Entropy in the Molecular Recognition of Membrane Protein-Lipid Interactions

Understanding the molecular driving forces that underlie membrane protein-lipid interactions requires the characterization of their binding thermodynamics. Here, we employ variable-temperature native mass spectrometry to determine the thermodynamics of lipid binding events to the human G-protein-gated inward rectifier potassium channel, Kir3.2. The channel displays distinct thermodynamic strategies to engage phosphatidylinositol (PI) and phosphorylated forms thereof. The addition of a 4'-phosphate to PI results in an increase in favorable entropy. PI with two or more phosphates exhibits more complex binding, where lipids appear to bind two nonidentical sites on Kir3.2. Remarkably, the interaction of 4,5-bisphosphate PI with Kir3.2 is solely driven by a large, favorable change in entropy. Installment of a 3'-phosphate to PI(4,5)P₂ results in an altered thermodynamic strategy. The acyl chain of the lipid has a marked impact on binding thermodynamics and, in some cases, enthalpy becomes favorable.

Insight into the Phospholipid-Binding Preferences of Kir3.4

The G-protein-gated inwardly rectifying potassium channel 4 (Kir3.4) subunit forms functional tetramers. Previous studies have established that phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) is required for Kir3.4 function. However, the binding preferences of Kir3.4 for the headgroup and acyl chains of phosphorylated phosphatidylinositides (PIPs) and other lipids are not well understood. Here, the interactions between full-length, human Kir3.4 and lipids are characterized using native mass spectrometry (MS) in conjunction with a soluble fluorescent lipid-binding assay. Kir3.4 displays binding preferences for PIPs, and, in some cases, the degree of binding is influenced by the type of acyl chains. The interactions between Kir3.4 and PIPs are weaker in comparison to full-length, human Kir3.2. The binding of PI(4,5)P₂ modified with a fluorophore to Kir3.2 can be enhanced by other lipids, such as phosphatidylcholine. Introduction of S143T, a mutation that enhances Kir3.4 activity, results in an overall reduction in the channel binding PIPs. In contrast, the D223N mutant of Kir3.4 that mimics the sodium-bound state exhibited stronger binding for PI(4,5)P₂, particularly for those with 18:0-20:4 acyl chains. Taken together, these results provide additional insight into the interaction between Kir3.4 and lipids that are important for channel function.

The Current State of Beta-Cell-Mass PET Imaging for Diabetes Research and Therapies

Diabetes is a chronic metabolic disease affecting over 400 million people worldwide and one of the leading causes of death, especially in developing nations. The disease is characterized by chronic hyperglycemia, caused by defects in the insulin secretion or action pathway. Current diagnostic methods measure metabolic byproducts of the disease such as glucose level, glycated hemoglobin (HbA1c), insulin or C-peptide levels, which are indicators of the beta-cell function. However, they inaccurately reflect the disease progression and provide poor longitudinal information. Beta-cell mass has been suggested as an alternative approach to study disease progression in correlation to beta-cell function, as it behaves differently in the diabetes physiopathology. Study of the beta-cell mass, however, requires highly invasive and potentially harmful procedures such as pancreatic biopsies, making diagnosis and monitoring of the disease tedious. Nuclear medical imaging techniques using radiation emitting tracers have been suggested as strong non-invasive tools for beta-cell mass. A highly sensitive and high-resolution technique, such as positron emission tomography, provides an ideal solution for the visualization of beta-cell mass, which is particularly essential for better characterization of a disease such as diabetes, and for estimating treatment effects towards regeneration of the beta-cell mass. Development of novel, validated biomarkers that are aimed at beta-cell mass imaging are thus highly necessary and would contribute to invaluable breakthroughs in the field of diabetes research and therapies. This review aims to describe the various biomarkers and radioactive probes currently available for positron emission tomography imaging of beta-cell mass, as well as highlight the need for precise quantification and visualization of the beta-cell mass for designing new therapy strategies and monitoring changes in the beta-cell mass during the progression of diabetes.

Molecular structure of an open human KATP channel

KATP channels are metabolic sensors that translate intracellular ATP/ADP balance into membrane excitability. The molecular composition of KATP includes an inward-rectifier potassium channel (Kir) and an ABC transporter-like sulfonylurea receptor (SUR). Although structures of KATP have been determined in many conformations, in all cases, the pore in Kir is closed. Here, we describe human pancreatic KATP (hKATP) structures with an open pore at 3.1- to 4.0-Å resolution using single-particle cryo-electron microscopy (cryo-EM). Pore opening is associated with coordinated structural changes within the ATP-binding site and the channel gate in Kir. Conformational changes in SUR are also observed, resulting in an area reduction of contact surfaces between SUR and Kir. We also observe that pancreatic hKATP exhibits the unique (among inward-rectifier channels) property of PIP2-independent opening, which appears to be correlated with a docked cytoplasmic domain in the absence of PIP2.

Copine 3 "CPNE3" is a novel regulator for insulin secretion and glucose uptake in pancreatic β-cells

Copine 3 (CPNE3) is a calcium-dependent phospholipid-binding protein that has been found to play an essential role in cancer progression and stages. However, its role in pancreatic β-cell function has not been investigated. Therefore, we performed a serial of bioinformatics and functional experiments to explore the potential role of Cpne3 on insulin secretion and β-cell function in human islets and INS-1 (832/13) cells. RNA sequencing and microarray data revealed that CPNE3 is highly expressed in human islets compared to other CPNE genes. In addition, expression of CPNE3 was inversely correlated with HbA1c and reduced in human islets from hyperglycemic donors. Silencing of Cpne3 in INS-1 cells impaired glucose-stimulated insulin secretion (GSIS), insulin content and glucose uptake efficiency without affecting cell viability or inducing apoptosis. Moreover, mRNA and protein expression of the key regulators in glucose sensing and insulin secretion (Insulin, GLUT2, NeuroD1, and INSR) were downregulated in Cpne3-silenced cells. Taken together, data from the present study provides a new understanding of the role of CPNE3 in maintaining normal β-cell function, which might contribute to developing a novel target for future management of type 2 diabetes therapy.

Early-Phase Luciferase Signals of Islet Grafts Predicts Successful Subcutaneous Site Transplantation in Rats

PURPOSE

The transplantation of pancreatic islets is a promising cell replacement therapy for type 1 diabetes. Subcutaneous islet transplantation is currently under investigation as a means to circumvent problems associated with standard intra-hepatic islet transplantation. As modifications are being developed to improve the efficacy of subcutaneous islet transplantation, it is important to have robust methods to assess engraftment. Experimentally, ATP-dependent bioluminescence imaging using luciferase reporter genes has been effective for non-invasively tracking engraftment. However, it was heretofore unknown if the bioluminescence of subcutaneously transplanted luciferase-expressing islet grafts correlates with diabetes reversal, a primary outcome of transplantation.

PROCEDURES

A retrospective analysis was conducted using data obtained from subcutaneous islet transplantations in Lewis rats. The analysis included transplantations from our laboratory in which islet donors were transgenic rats ubiquitously expressing luciferase and recipients were wild type, streptozotocin-induced diabetic rats. Data from 79 bioluminescence scans were obtained from 27 islet transplantations during the post-transplant observation period (up to 6 weeks). The bioluminescence intensity of the subcutaneously transplanted grafts, captured after the intravenous administration of luciferin, was correlated with diabetes reversal.

RESULTS

After subcutaneous transplantation, islet bioluminescence decreased over time, dropping > 50 % from 1 to 3 weeks post-transplant. Bioluminescence intensity in the early post-transplant phase (1-2 weeks) correlated with the subsequent reversal of diabetes; based on optimized bioluminescence cutoff values, the bioluminescence intensity of islets at 1 and 2 weeks predicted successful transplantations. However, intensity in the late post-transplant phase (≥ 4 weeks) did not reflect transplantation outcomes.

CONCLUSIONS

Early-phase bioluminescence imaging of luciferase-expressing islets could serve as a useful tool to predict the success of subcutaneous islet transplantations by preceding changes in glucose homeostasis.

Antipsychotics inhibit the mitochondrial bioenergetics of pancreatic beta cells isolated from CD1 mice

Antipsychotics (APs) are widely used medications with reported diabetogenic side effects. This study investigated the effect of commonly used APs, namely chlorpromazine (CPZ), haloperidol (HAL) and clozapine, on the bioenergetics of male CD1 mice isolated pancreatic beta cells as an underlying mechanism of their diabetogenic effects. The effect of APs on Alamar blue reduction, adenosine triphosphate (ATP) production and glucose-stimulated insulin secretion (GSIS) of isolated beta cells was evaluated. Then, the effects of APs on the activities of mitochondrial complexes and their common coding genes expression, oxygen consumption rate (OCR), mitochondrial membrane potential (MMP) and lactate production were investigated. The effects of APs on the mitochondrial membrane fluidity (MMF) and mitochondrial membrane fatty acid composition were also examined. Results showed that the tested APs significantly decreased cellular ATP production and GSIS of the beta cells. The APs significantly inhibited the activities of mitochondrial complexes and their coding gene expression, MMP and OCR of the treated cells, with a parallel increase in lactate production to different extents with the different APs. CPZ and HAL showed increased MMF and mitochondrial membrane polyunsaturated fatty acid content. In conclusion, the tested APs-induced mitochondrial disruption can play a role in their diabetogenic side effect.

Pleiotropic use of Statins as non-lipid-lowering drugs

Statins, known as HMG-CoA reductase (HMGCR) inhibitors, have primarily been utilized for metabolic and angiographic medical applications because of their cholesterol-lowering effects. Similar to other drugs, statins may also induce a series of potential side effects. Statins inhibit the HMGCR (rate-limiting enzyme) activity in early stages of mevalonate pathway and then indirectly affect a number of intermediate products, including non-sterol isoprenoids (coenzyme Q10, dolichol etc.), which can result in impaired functions of body organs. Recently, scores of studies have uncovered additional functional mechanisms of statins in other diseases, such as diabetes mellitus, nervous system diseases, coronary heart disease, inflammation and cancers. This review aims to summarize the positive and adverse mechanisms of statin therapy. Statin care should be taken in the treatment of many diseases including cancers. Since the underlying mechanisms are not fully elucidated, future studies should spend more time and efforts on basic research to explore the mechanisms of statins.

Untargeted Metabolomic Approach Shows No Differences in Subcutaneous Adipose Tissue of Diabetic and Non-Diabetic Subjects Undergoing Bariatric Surgery: An Exploratory Study

BACKGROUND

Obesity plays a major role in the development of insulin resistance (IR) and diabetes (T2DM). Increased adipose tissue (AT) is particularly of interest because it activates a chronic inflammatory response in adipocytes and other tissues. AT plays key endocrine and metabolic functions, acting in the regulation of insulin sensitivity and energy homeostasis. Additionally, it can be easily collected during bariatric surgery. The purpose of this pilot study was to explore the potential differences in AT metabolism, through comparing the untargeted metabolomic profiles of diabetic and non-diabetic obese patients undergoing bariatric surgery.

METHODS

For this exploratory study, samples were collected from 17 subjects. Subcutaneous AT (SAT) samples from obese-diabetic (n = 8) and Obese-non-Diabetic (n = 9) subjects were obtained from the Human Metabolic Tissue Bank. Untargeted metabolomic profiling was performed by Metabolon® Inc. Statistical analysis was performed using the MetaboAnalyst 4.0 platform.

RESULTS

Among the 421 metabolites identified and analyzed there were no significant differences between the Obese-Diabetics and the Obese-non-Diabetics. Small changes were observed by fold change analysis mainly in lipid (n = 12; e.g. NEFAs) and amino acid (n = 8; e.g. BCAAs) metabolic pathways. Dysregulation of these metabolites has been associated with IR and other T2DM-related pathophysiological processes.

CONCLUSION

Obesity may influence SAT metabolism masking T2DM-dependent dysregulation. Better understanding the metabolic differences within SAT in diabetic populations may help identify potential biomarkers for diagnosis and monitoring of T2DM in patients undergoing bariatric surgery.

Targeted pancreatic beta cell imaging for early diagnosis

Pancreatic beta cells are important in blood glucose level regulation. As type 1 and 2 diabetes are getting prevalent worldwide, we need to explore new methods for early detection of beta cell-related afflictions. Using bioimaging techniques to measure beta cell mass is crucial because a decrease in beta cell density is seen in diseases such as diabetes and thus can be a new way of diagnosis for such diseases. We also need to appraise beta cell purity in transplanted islets for type 1 diabetes patients. Sufficient amount of functional beta cells must also be determined before being transplanted to the patients. In this review, indirect imaging of beta cells will be discussed. This includes membrane protein on pancreatic beta cells whereby specific probes are designed for different imaging modalities mainly magnetic resonance imaging, positron emission tomography and fluorescence imaging. Direct imaging of insulin is also explored though probes synthesized for such function are relatively fewer. The path for successful pancreatic beta cell imaging is fraught with challenges like non-specific binding, lack of beta cell-restricted targets, the requirement of probes to cross multiple lipid layers to bind to intracellular insulin. Hence, there is an urgent need to develop new imaging techniques and innovative probing constructs in the entire imaging chain of bioengineering to provide early detection of beta cell-related pathology.

Perfluorooctane sulfonate acute exposure stimulates insulin secretion via GPR40 pathway

Perfluoroalkyl substances (PFASs) are widely used synthetic chemicals, showing environmental/biological persistence and adverse effects on ecosystem and human health. Several epidemiological and animal studies have revealed that PFASs levels are associated with elevated serum insulin level; however, the effect of PFASs on insulin secretion and the underlying mechanism are not clear. In this study, the effect of a most concerned PFAS, perfluorooctane sulfonate (PFOS) on insulin secretion in Beta-TC-6 pancreatic cells was studied. The results showed that PFOS acute exposure stimulated insulin secretion and elevated intracellular calcium concentration ([Ca²⁺]_i). The PFOS-stimulated [Ca²⁺]_i elevation was resulted from both extra- and intra-cellular sources. PFOS acute exposure decreased ATP content and ATP/ADP ratio, indicating the mitochondrial function was damaged under PFOS acute exposure. The PFOS-stimulated insulin secretion was inhibited by GW1100, a G Protein-coupled Receptor 40 (GPR40) specific inhibitor, but not affected by GW9662, a specific antagonist to the peroxisome proliferator-activated receptor gamma (PPARγ). The observation of RNA silencing further demonstrated that the PFOS-stimulated insulin secretion is, at least partially, via GPR40. By using specific inhibitors, we found that the GPR40 downstream pathways, phospholipase C (PLC) and L-type Ca²⁺ channels (LTCC) were involved in PFOS-stimulated [Ca²⁺]_i elevation and insulin secretion.

Transcriptomic analysis by RNA sequencing characterises malignant progression of canine insulinoma from normal tissue to metastatic disease

Insulinomas (INS) are the most common human and canine functioning pancreatic neuroendocrine tumours. The long-term prognosis for malignant INS is poor, because micrometastases are frequently missed during surgery. As human and canine malignant INS share clinical and histopathological features, dogs have been proposed as models for INS research. Using RNA-sequencing, we conducted a pilot study to better understand the underlying molecular mechanisms of canine INS. Normal canine pancreas and lymph node control tissues were compared with primary INS and INS-metastatic lymph nodes, revealing more than 3,000 genes differentially expressed in normal pancreas compared to primary INS. Only 164 genes were differentially expressed between primary INS and INS-metastatic lymph nodes. Hierarchical clustering analysis demonstrated similar genetic profiles in normal pancreas and early clinical stage primary INS, whereas late clinical stage primary INS resembled the genetic profile of INS-metastatic lymph nodes. These findings suggest that markers of malignant behaviour could be identified at the primary site of the disease. Finally, using the REACTOME pathways database, we revealed that an active collagen metabolism, extracellular matrix remodelling, beta-cell differentiation and non-beta-cell trans-differentiation might cause disease progression and hyperinsulinism in INS, identifying major pathways worthy of future research in this currently poorly controlled disease.

A computational structural biology study to understand the impact of mutation on structure-function relationship of inward-rectifier potassium ion channel Kir6.2 in human

Type 2 diabetes (T2D) is clinically characterized via hyperglycemia. Polymorphism rs5219 in the KCNJ11 gene is a risk factor for developing T2D in humans. KCNJ11 encodes the 'inward-rectifier potassium ion channel (Kir6.2)'. However, because of the absence of the complete crystal/NMR structures of Kir6.2 proteins, insight into its structure and function and its interaction with diverse ligands remain elusive to date. Therefore, a computational approach was employed for predicting the best plausible 'three-dimensional' structure of Kir6.2 as well as for studying the influence of mutation (p. GLU23LYS) on both architectures as well as the function of Kir6.2 employing simulation studies. Results obtained revealed that though, with increased time, 'Gibbs free energy' becomes positive, residues in wild type Kir6.2 experiences less random movement as compared to mutant Kir6.2. The less random movement of residues in wild type Kir6.2 represents the standard coupling between open and closing of 'K_ATP channel' and thus the normal secretion of insulin. The more dispersed motion of mutant Kir6.2 residues represents 'overactivity' of the 'K_ATP channel' and thus insulin 'under-secretion'. Further, molecular docking and simulation studies identified two phytochemicals/drugs, namely, A-348441 and chushizisin I, which retains the wild type property of Kir6.2 after binding with mutant protein. Unlike A-348441, this is for the first time, the present study is reporting about the plausible anti-diabetic property of chushizisin I. As these two phytochemicals/drugs, namely, A-348441 and chushizisin I, have passed ADMET test, in the near future, they may be utilized as anti-diabetic drugs after further investigation.Communicated by Ramaswamy H. Sarma.

Gut Peptide Agonism in the Treatment of Obesity and Diabetes

Obesity is a global healthcare challenge that gives rise to devastating diseases such as the metabolic syndrome, type-2 diabetes (T2D), and a variety of cardiovascular diseases. The escalating prevalence of obesity has led to an increased interest in pharmacological options to counteract excess weight gain. Gastrointestinal hormones such as glucagon, amylin, and glucagon-like peptide-1 (GLP-1) are well recognized for influencing food intake and satiety, but the therapeutic potential of these native peptides is overall limited by a short half-life and an often dose-dependent appearance of unwanted effects. Recent clinical success of chemically optimized GLP-1 mimetics with improved pharmacokinetics and sustained action has propelled pharmacological interest in using bioengineered gut hormones to treat obesity and diabetes. In this article, we summarize the basic biology and signaling mechanisms of selected gut peptides and discuss how they regulate systemic energy and glucose metabolism. Subsequently, we focus on the design and evaluation of unimolecular drugs that combine the beneficial effects of selected gut hormones into a single entity to optimize the beneficial impact on systems metabolism. © 2020 American Physiological Society. Compr Physiol 10:99-124, 2020.

Mechanism of pharmacochaperoning in a mammalian KATP channel revealed by cryo-EM

ATP-sensitive potassium (K_ATP) channels composed of a pore-forming Kir6.2 potassium channel and a regulatory ABC transporter sulfonylurea receptor 1 (SUR1) regulate insulin secretion in pancreatic β-cells to maintain glucose homeostasis. Mutations that impair channel folding or assembly prevent cell surface expression and cause congenital hyperinsulinism. Structurally diverse K_ATP inhibitors are known to act as pharmacochaperones to correct mutant channel expression, but the mechanism is unknown. Here, we compare cryoEM structures of a mammalian K_ATP channel bound to pharmacochaperones glibenclamide, repaglinide, and carbamazepine. We found all three drugs bind within a common pocket in SUR1. Further, we found the N-terminus of Kir6.2 inserted within the central cavity of the SUR1 ABC core, adjacent the drug binding pocket. The findings reveal a common mechanism by which diverse compounds stabilize the Kir6.2 N-terminus within SUR1’s ABC core, allowing it to act as a firm ‘handle’ for the assembly of metastable mutant SUR1-Kir6.2 complexes.

Beta-cell excitability and excitability-driven diabetes in adult Zebrafish islets

Islet β-cell membrane excitability is a well-established regulator of mammalian insulin secretion, and defects in β-cell excitability are linked to multiple forms of diabetes. Evolutionary conservation of islet excitability in lower organisms is largely unexplored. Here we show that adult zebrafish islet calcium levels rise in response to elevated extracellular [glucose], with similar concentration-response relationship to mammalian β-cells. However, zebrafish islet calcium transients are nor well coupled, with a shallower glucose-dependence of cytoplasmic calcium concentration. We have also generated transgenic zebrafish that conditionally express gain-of-function mutations in ATP-sensitive K+ channels (KATP -GOF) in β-cells. Following induction, these fish become profoundly diabetic, paralleling features of mammalian diabetes resulting from equivalent mutations. KATP -GOF fish become severely hyperglycemic, with slowed growth, and their islets lose glucose-induced calcium responses. These results indicate that, although lacking tight cell-cell coupling of intracellular Ca2+ , adult zebrafish islets recapitulate similar excitability-driven β-cell glucose responsiveness to those in mammals, and exhibit profound susceptibility to diabetes as a result of inexcitability. While illustrating evolutionary conservation of islet excitability in lower vertebrates, these results also provide important validation of zebrafish as a suitable animal model in which to identify modulators of islet excitability and diabetes.

Successful Use of Octreotide Therapy for Refractory Levofloxacin-Induced Hypoglycemia: A Case Report and Literature Review

Fluoroquinolones are commonly prescribed antimicrobials that have been implicated in alterations of glucose metabolism. We report a case of refractory fluoroquinolone-induced hypoglycemia in a patient with type-2 diabetes mellitus on glipizide that was successfully treated with octreotide. A patient was admitted with hypoglycemia after having been initiated on levofloxacin therapy. Despite treating the hypoglycemia supportively with multiple boluses of 25 g of dextrose, a continuous dextrose infusion, and glucagon, the patient experienced repeated episodes of rebound hypoglycemia. The persistent hypoglycemia was eventually reversed with the administration of subcutaneous octreotide. Clinicians should be cognizant of this adverse effect of fluoroquinolones, as well as predisposing risk factors, and consider octreotide as an adjunctive therapy for refractory hypoglycemia cases.

Diabetes pharmacotherapy and effects on the musculoskeletal system

Persons with type 1 or type 2 diabetes have a significantly higher fracture risk than age-matched persons without diabetes, attributed to disease-specific deficits in the microarchitecture and material properties of bone tissue. Therefore, independent effects of diabetes drugs on skeletal integrity are vitally important. Studies of incretin-based therapies have shown divergent effects of different agents on fracture risk, including detrimental, beneficial, and neutral effects. The sulfonylurea class of drugs, owing to its hypoglycemic potential, is thought to amplify the risk of fall-related fractures, particularly in the elderly. Other agents such as the biguanides may, in fact, be osteo-anabolic. In contrast, despite similarly expected anabolic properties of insulin, data suggests that insulin pharmacotherapy itself, particularly in type 2 diabetes, may be a risk factor for fracture, negatively associated with determinants of bone quality and bone strength. Finally, sodium-dependent glucose co-transporter 2 inhibitors have been associated with an increased risk of atypical fractures in select populations, and possibly with an increase in lower extremity amputation with specific SGLT2I drugs. The role of skeletal muscle, as a potential mediator and determinant of bone quality, is also a relevant area of exploration. Currently, data regarding the impact of glucose lowering medications on diabetes-related muscle atrophy is more limited, although preclinical studies suggest that various hypoglycemic agents may have either aggravating (sulfonylureas, glinides) or repairing (thiazolidinediones, biguanides, incretins) effects on skeletal muscle atrophy, thereby influencing bone quality. Hence, the therapeutic efficacy of each hypoglycemic agent must also be evaluated in light of its impact, alone or in combination, on musculoskeletal health, when determining an individualized treatment approach. Moreover, the effect of newer medications (potentially seeking expanded clinical indication into the pediatric age range) on the growing skeleton is largely unknown. Herein, we review the available literature regarding effects of diabetes pharmacotherapy, by drug class and/or by clinical indication, on the musculoskeletal health of persons with diabetes.

Kir2.1 is important for efficient BMP signaling in mammalian face development

Mutations that disrupt the inwardly rectifying potassium channel Kir2.1 lead to Andersen-Tawil syndrome that includes periodic paralysis, cardiac arrhythmia, cognitive deficits, craniofacial dysmorphologies and limb defects. The molecular mechanism that underlies the developmental consequences of inhibition of these channels has remained a mystery. We show that while loss of Kir2.1 function does not affect expression of several early facial patterning genes, the domain in which Pou3f3 is expressed in the maxillary arch is reduced. Pou3f3 is important for development of the jugal and squamosal bones. The reduced expression domain of Pou3f3 is consistent with the reduction in the size of the squamosal and jugal bones in Kcnj2KO/KO animals, however it does not account for the diverse craniofacial defects observed in Kcnj2KO/KO animals. We show that Kir2.1 function is required in the cranial neural crest for morphogenesis of several craniofacial structures including palate closure. We find that while the palatal shelves of Kir2.1-null embryos elevate properly, they are reduced in size due to decreased proliferation of the palatal mesenchyme. While we find no reduction in expression of BMP ligands, receptors, and associated Smads in this setting, loss of Kir2.1 reduces the efficacy of BMP signaling as shown by the reduction of phosphorylated Smad 1/5/8 and reduced expression of BMP targets Smad6 and Satb2.

The biologic effect of hydrogen sulfide and its function in various diseases

INTRODUCTION

Hydrogen sulfide (H2S), a colorless, water soluble, flammable gas with a characteristic smell of rotten eggs, has been known as a highly toxic gas for several years. However, much like carbon monoxide (CO) and nitric oxide (NO), the initial negative perception of H2S has developed with the discovery that H2S is generated enzymatically in animals under normal conditions. With the result of this discovery, much more work is needed to elucidate the biologic effects of H2S. In recent years, its cytoprotective properties have been recognized in multiple organs and tissues. In particular, H2S plays important roles in combating oxidative species such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) and protect the body from oxidative stress. Therefore, this review discusses the biologic effect of H2S and how it protects cells in various diseases by acting as an antioxidant that reduces excessive amounts of ROS and RNS.

ETHICS AND DISSEMINATION

Ethical approval and informed consent are not required, as the study will be a literature review and will not involve direct contact with patients or alterations to patient care.

CONCLUSION

H2S has been found to be cytoprotective in oxidative stress in a wide range of physiologic and pathologic conditions, an increasing number of therapeutic potentials of H2S also have been revealed. However, there is still much debate on the clear mechanism of action of H2S, so that the mechanisms of cell signaling that promote cellular survival and organ protection need to be further investigated to provide better H2S-based therapeutics.

Memantine has no effect on KATP channels in pancreatic β cells

Objective

Memantine, a drug for Alzheimer’s disease, is considered to suppress excessive stimulation of N-methyl-d-aspartic acid receptors and to prevent neuronal death. However, a recent report indicated that the neuronal K_ATP channel also can become a target of memantine. The K_ATP channel is a key regulator of insulin secretion in pancreatic β cells. Therefore, if memantine could inhibit the K_ATP channel in pancreatic β cells, it would be an effective drug for both Alzheimer’s disease and diabetes. However, there is no report on the effect of memantine on the K_ATP channel in pancreatic β cells. Therefore, we investigated whether memantine affect the blood glucose level, insulin secretion and K_ATP channel activity in pancreatic β cells.

Results

An intraperitoneal glucose tolerance test was performed with or without memantine (1 mg/kg) injection in intact mice. Insulin secretion from isolated islets was measured under low (2 mM) and high (20 mM) glucose concentrations with or without memantine (1 μM). The effect of memantine (1 μM) on K_ATP channel currents in isolated pancreatic β cells was recorded using the whole-cell patch-clamp technique. Memantine had no effect on the blood glucose level, insulin secretion from isolated islets or K_ATP channel current in pancreatic β cells.

Gliclazide, a KATP channel blocker, inhibits vascular smooth muscle cell proliferation through the CaMKKβ-AMPK pathway

Gliclazide, a sulfonylurea that is widely used to treat type II-diabetes, specifically blocks K_ATP channels and recombinant smooth muscle (SUR2B/Kir6.1) K_ATP channels with high potency. Furthermore, it exerts antioxidant properties and inhibits tumor cell proliferation. In this study, we investigated the inhibitory effect of gliclazide on vascular smooth muscle cell (VSMC) proliferation and tried to identify the underlying signaling pathway. We first investigated the effect of gliclazide-induced AMP-activated protein kinase (AMPK) activation on the proliferation of VSMCs. Gliclazide induced phosphorylation of AMPK in a dose- and time-dependent manner and inhibited VSMC proliferation following stimulation by platelet-derived growth factor (PDGF). However, K_ATP channel openers and Kir6.1 siRNA prevented gliclazide-mediated inhibition of VSMC proliferation. Gliclazide also increased the levels of Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ), an upstream kinase of AMPK. These findings suggested that the effects of K_ATP channels on AMPK activity were mediated by the regulation of intracellular Ca²⁺ levels. Oral administration of 2mg/kg gliclazide resulted in the activation of CaMKKβ and AMPK in vivo, suggesting that gliclazide suppressed VSMC proliferation via the CaMKKβ-AMPK signaling pathway. Taken together, our observations indicated that gliclazide-induced AMPK activation may act to prevent diabetes-associated atherosclerosis.

Sulfonylurea challenge test in subjects diagnosed with type 1 diabetes mellitus

BACKGROUND

Patients with early onset diabetes because of defects in glucose-stimulated insulin secretion (GSIS) may respond better to sulfonylureas than insulin treatment. Such patients include those with monogenic disorders, who can be differentiated from autoimmune type 1 diabetes mellitus (T1DM) by genetic testing. Genetic testing is expensive and unknown defects in GSIS would not be diagnosed.

AIMS

We propose a sulfonylurea challenge test to identify patients who have been clinically diagnosed with T1DM, but those who maintain a preferentially sulfonylurea-responsive insulin secretion.

MATERIALS & METHODS

A total of 3 healthy controls, 2 neonatal diabetes mellitus (NDM) subjects, 3 antibody-positive (Ab+T1DM), and 12 antibody-negative (Ab-T1DM) subjects with type 1 diabetes, were given an intravenous bolus of glucose followed by an oral dose of glipizide.

RESULTS

Healthy controls showed a robust C-peptide increase after both glucose and glipizide, but NDM subjects showed a large increase in C-peptide only following glipizide. As expected, 2 of 3 Ab+T1DM, as well as 11 of 12 Ab-T1DM showed no response to either glucose or glipizide. However, 1 Ab-T1DM and 1 Ab+T1DM showed a small C-peptide response to glucose and a marked positive response to glipizide, suggesting defects in GSIS rather than typical autoimmune diabetes.

DISCUSSION

These data demonstrate the feasibility of the sulfonylurea challenge test, and suggest that responder individuals may be identified.

CONCLUSIONS

We propose that this sulfonylurea challenge test should be explored more extensively, as it may prove useful as a clinical and scientific tool.

Current Therapies That Modify Glucagon Secretion: What Is the Therapeutic Effect of Such Modifications?

PURPOSE OF REVIEW

Hyperglucagonemia contributes significantly to hyperglycemia in type 2 diabetes and suppressed glucagon levels may increase the risk of hypoglycemia. Here, we give a brief overview of glucagon physiology and the role of glucagon in the pathophysiology of type 2 diabetes and provide insights into how antidiabetic drugs influence glucagon secretion as well as a perspective on the future of glucagon-targeting drugs.

RECENT FINDINGS

Several older as well as recent investigations have evaluated the effect of antidiabetic agents on glucagon secretion to understand how glucagon may be involved in the drugs' efficacy and safety profiles. Based on these findings, modulation of glucagon secretion seems to play a hitherto underestimated role in the efficacy and safety of several glucose-lowering drugs. Numerous drugs currently available to diabetologists are capable of altering glucagon secretion: metformin, sulfonylurea compounds, insulin, glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase-4 inhibitors, sodium-glucose cotransporter 2 inhibitors and amylin mimetics. Their diverse effects on glucagon secretion are of importance for their individual efficacy and safety profiles. Understanding how these drugs interact with glucagon secretion may help to optimize treatment.

Anti-diabetic drug binding site in a mammalian KATP channel revealed by Cryo-EM

Sulfonylureas are anti-diabetic medications that act by inhibiting pancreatic K_ATP channels composed of SUR1 and Kir6.2. The mechanism by which these drugs interact with and inhibit the channel has been extensively investigated, yet it remains unclear where the drug binding pocket resides. Here, we present a cryo-EM structure of a hamster SUR1/rat Kir6.2 channel bound to a high-affinity sulfonylurea drug glibenclamide and ATP at 3.63 Å resolution, which reveals unprecedented details of the ATP and glibenclamide binding sites. Importantly, the structure shows for the first time that glibenclamide is lodged in the transmembrane bundle of the SUR1-ABC core connected to the first nucleotide binding domain near the inner leaflet of the lipid bilayer. Mutation of residues predicted to interact with glibenclamide in our model led to reduced sensitivity to glibenclamide. Our structure provides novel mechanistic insights of how sulfonylureas and ATP interact with the K_ATP channel complex to inhibit channel activity.

Expression and function of ATP-dependent potassium channels in zebrafish islet β-cells

ATP-sensitive potassium channels (KATP channels) are critical nutrient sensors in many mammalian tissues. In the pancreas, KATP channels are essential for coupling glucose metabolism to insulin secretion. While orthologous genes for many components of metabolism-secretion coupling in mammals are present in lower vertebrates, their expression, functionality and ultimate impact on body glucose homeostasis are unclear. In this paper, we demonstrate that zebrafish islet β-cells express functional KATP channels of similar subunit composition, structure and metabolic sensitivity to their mammalian counterparts. We further show that pharmacological activation of native zebrafish KATP using diazoxide, a specific KATP channel opener, is sufficient to disturb glucose tolerance in adult zebrafish. That β-cell KATP channel expression and function are conserved between zebrafish and mammals illustrates the evolutionary conservation of islet metabolic sensing from fish to humans, and lends relevance to the use of zebrafish to model islet glucose sensing and diseases of membrane excitability such as neonatal diabetes.

Natural Triterpenoids for the Treatment of Diabetes Mellitus: A Review

Triterpenoids, an important group of secondary metabolites, are widely distributed in nature. Many triterpenoids have been found with potential therapeutic effect against diabetes mellitus. However, the use of triterpenoids for the treatment of diabetes has not been systematically discussed previously. This review summarized the anti-diabetic activity of natural triterpenoids reported since the late 1980s with the emphasis on the molecular mechanisms.

Implications of Hydrogen Sulfide in Glucose Regulation: How H2S Can Alter Glucose Homeostasis through Metabolic Hormones

Diabetes and its comorbidities continue to be a major health problem worldwide. Understanding the precise mechanisms that control glucose homeostasis and their dysregulation during diabetes are a major research focus. Hydrogen sulfide (H₂S) has emerged as an important regulator of glucose homeostasis. This is achieved through its production and action in several metabolic and hormone producing organs including the pancreas, liver, and adipose. Of importance, H₂S production and signaling in these tissues are altered during both type 1 and type 2 diabetes mellitus. This review first examines how H₂S is produced both endogenously and by gastrointestinal microbes, with a particular focus on the altered production that occurs during obesity and diabetes. Next, the action of H₂S on the metabolic organs with key roles in glucose homeostasis, with a particular focus on insulin, is described. Recent work has also suggested that the effects of H₂S on glucose homeostasis goes beyond its role in insulin secretion. Several studies have demonstrated important roles for H₂S in hepatic glucose output and adipose glucose uptake. The mechanism of H₂S action on these metabolic organs is described. In the final part of this review, future directions examining the roles of H₂S in other metabolic and glucoregulatory hormone secreting tissues are proposed.

IGF-1 Receptor Differentially Regulates Spontaneous and Evoked Transmission via Mitochondria at Hippocampal Synapses

The insulin-like growth factor-1 receptor (IGF-1R) signaling is a key regulator of lifespan, growth, and development. While reduced IGF-1R signaling delays aging and Alzheimer's disease progression, whether and how it regulates information processing at central synapses remains elusive. Here, we show that presynaptic IGF-1Rs are basally active, regulating synaptic vesicle release and short-term plasticity in excitatory hippocampal neurons. Acute IGF-1R blockade or transient knockdown suppresses spike-evoked synaptic transmission and presynaptic cytosolic Ca(2+) transients, while promoting spontaneous transmission and resting Ca(2+) level. This dual effect on transmitter release is mediated by mitochondria that attenuate Ca(2+) buffering in the absence of spikes and decrease ATP production during spiking activity. We conclude that the mitochondria, activated by IGF-1R signaling, constitute a critical regulator of information processing in hippocampal neurons by maintaining evoked-to-spontaneous transmission ratio, while constraining synaptic facilitation at high frequencies. Excessive IGF-1R tone may contribute to hippocampal hyperactivity associated with Alzheimer's disease.

Potentiation of Calcium Influx and Insulin Secretion in Pancreatic Beta Cell by the Specific TREK-1 Blocker Spadin

Inhibition of the potassium channels TREK-1 by spadin (SPA) is currently thought to be a promising therapeutic target for the treatment of depression. Since these channels are expressed in pancreatic β-cells, we investigated their role in the control of insulin secretion and glucose homeostasis. In this study, we confirmed the expression of TREK-1 channels in the insulin secreting MIN6-B1 β-cell line and in mouse islets. We found that their blockade by SPA potentiated insulin secretion induced by potassium chloride dependent membrane depolarization. Inhibition of TREK-1 by SPA induced a decrease of the resting membrane potential (ΔV_m ~ 12 mV) and increased the cytosolic calcium concentration. In mice, administration of SPA enhanced the plasma insulin level stimulated by glucose, confirming its secretagogue effect observed in vitro. Taken together, this work identifies SPA as a novel potential pharmacological agent able to control insulin secretion and glucose homeostasis.

Electrophysiologic consequences of KATP gain of function in the heart: Conduction abnormalities in Cantu syndrome

BACKGROUND

Gain-of-function (GOF) mutations in the KATP channel subunits Kir6.1 and SUR2 cause Cantu syndrome (CS), a disease characterized by multiple cardiovascular abnormalities.

OBJECTIVE

The purpose of this study was to better determine the electrophysiologic consequences of such GOF mutations in the heart.

METHODS

We generated transgenic mice (Kir6.1-GOF) expressing ATP-insensitive Kir6.1[G343D] subunits under α-myosin heavy chain (α-MHC) promoter control, to target gene expression specifically in cardiomyocytes, and performed patch-clamp experiments on isolated ventricular myocytes and invasive electrophysiology on anesthetized mice.

RESULTS

In Kir6.1-GOF ventricular myocytes, KATP channels showed decreased ATP sensitivity but no significant change in current density. Ambulatory ECG recordings on Kir6.1-GOF mice revealed AV nodal conduction abnormalities and junctional rhythm. Invasive electrophysiologic analyses revealed slowing of conduction and conduction failure through the AV node but no increase in susceptibility to atrial or ventricular ectopic activity. Surface ECGs recorded from CS patients also demonstrated first-degree AV block and fascicular block.

CONCLUSION

The primary electrophysiologic consequence of cardiac KATP GOF is on the conduction system, particularly the AV node, resulting in conduction abnormalities in CS patients who carry KATP GOF mutations.

Esculentin-2CHa-Related Peptides Modulate Islet Cell Function and Improve Glucose Tolerance in Mice with Diet-Induced Obesity and Insulin Resistance

The frog skin host-defense peptide esculentin-2CHa (GFSSIFRGVA¹⁰KFASKGLGK D²⁰LAKLGVDLVA³⁰CKISKQC) displays antimicrobial, antitumor, and immunomodulatory properties. This study investigated the antidiabetic actions of the peptide and selected analogues. Esculentin-2CHa stimulated insulin secretion from rat BRIN-BD11 clonal pancreatic β-cells at concentrations greater than 0.3 nM without cytotoxicity by a mechanism involving membrane depolarization and increase of intracellular Ca²⁺. Insulinotropic activity was attenuated by activation of K_ATP channels, inhibition of voltage-dependent Ca²⁺ channels and chelation of extracellular Ca²⁺. The [L21K], [L24K], [D20K, D27K] and [C31S,C37S] analogues were more potent but less effective than esculentin-2CHa whereas the [L28K] and [C31K] analogues were both more potent and produced a significantly (P < 0.001) greater maximum response. Acute administration of [L28K]esculentin-2CHa (75 nmol/kg body weight) to high fat fed mice with obesity and insulin resistance enhanced glucose tolerance and insulin secretion. Twice-daily administration of this dose of [L28K]esculentin-2CHa for 28 days had no significant effect on body weight, food intake, indirect calorimetry or body composition. However, mice exhibited decreased non-fasting plasma glucose (P < 0.05), increased non-fasting plasma insulin (P < 0.05) as well as improved glucose tolerance and insulin secretion (P < 0.01) following both oral and intraperitoneal glucose loads. Impaired responses of isolated islets from high fat fed mice to established insulin secretagogues were restored by [L28K]esculentin-2CHa treatment. Peptide treatment was accompanied by significantly lower plasma and pancreatic glucagon levels and normalization of α-cell mass. Circulating triglyceride concentrations were decreased but plasma cholesterol and LDL concentrations were not significantly affected. The data encourage further investigation of the potential of esculentin-2CHa related peptides for treatment of patients with type 2 diabetes.