The Sulfonylurea Receptor, an Atypical ATP-Binding Cassette Protein, and Its Regulation of the KATPChannel

Pathophysiology and Advances in the Therapy of Cardiomyopathy in Patients with Diabetes Mellitus

Diabetes mellitus (DM) is known as the first non-communicable global epidemic. It is estimated that 537 million people have DM, but the condition has been properly diagnosed in less than half of these patients. Despite numerous preventive measures, the number of DM cases is steadily increasing. The state of chronic hyperglycaemia in the body leads to numerous complications, including diabetic cardiomyopathy (DCM). A number of pathophysiological mechanisms are behind the development and progression of cardiomyopathy, including increased oxidative stress, chronic inflammation, increased synthesis of advanced glycation products and overexpression of the biosynthetic pathway of certain compounds, such as hexosamine. There is extensive research on the treatment of DCM, and there are a number of therapies that can stop the development of this complication. Among the compounds used to treat DCM are antiglycaemic drugs, hypoglycaemic drugs and drugs used to treat myocardial failure. An important element in combating DCM that should be kept in mind is a healthy lifestyle-a well-balanced diet and physical activity. There is also a group of compounds-including coenzyme Q10, antioxidants and modulators of signalling pathways and inflammatory processes, among others-that are being researched continuously, and their introduction into routine therapies is likely to result in greater control and more effective treatment of DM in the future. This paper summarises the latest recommendations for lifestyle and pharmacological treatment of cardiomyopathy in patients with DM.

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

Effects of treatment for diabetes mellitus on testosterone concentrations: A systematic review

BACKGROUND

Low testosterone levels are frequently present in men with obesity and insulin resistance. Currently available treatment options (testosterone replacement therapy or lifestyle changes) hold possible risks or are insufficient. Since low testosterone levels are closely related to obesity and type 2 diabetes, treatment modalities for these conditions could result into improvement of testosterone levels.

OBJECTIVES

To summarize the available evidence on the effects of traditional and recent treatment modalities for diabetes mellitus on testosterone levels and androgen-deficiency-related signs and symptoms.

MATERIALS AND METHODS

PubMed was searched from the year 2000 till present using MESH terms: "hypogonadism," "testosterone," "testosterone deficiency," "functional hypogonadism," and the different classes of medications. Studies with observational and experimental designs on humans that evaluated the effect of antidiabetic medications on gonadotropins and testosterone were eligible for inclusion.

RESULTS

Current available data show no or only limited improvement on testosterone levels with the classic antidiabetic drugs. Studies with GLP1-receptor analogues show beneficial effects on both body weight and testosterone levels in men with low testosterone levels and obesity with or without type 2 diabetes. However, data are limited to small and heterogeneous study groups and only few studies report data about impact on androgen-deficiency-related signs and symptoms.

DISCUSSION AND CONCLUSION

With the recent advances in the knowledge of the pathophysiological pathways in obesity, there is an enormous progress in the development of medications for obesity and type 2 diabetes. Newer incretin-based agents have a great potential for the treatment of functional hypogonadism due to obesity since they show promising weight reducing results. However, before the use of GLP1-receptor analogues can be suggested to treat functional hypogonadism, further studies are needed.

The Role of ABC Transporters in Skin Cells Exposed to UV Radiation

ABC transporters are expressed in skin cells to protect them against harmful xenobiotics. Moreover, these transmembrane proteins have a number of additional functions that ensure skin homeostasis. This review summarizes the current knowledge about the role of specific ABC proteins in the skin, including multi-drug resistance transporters (MDR1/3), the transporter associated with antigen processing 1/2 (TAP1/2), the cystic fibrosis transmembrane conductance regulator (CFTR), sulfonylurea receptors (SUR1/2), and the breast cancer resistance protein (BCRP). Additionally, the effect of UV radiation on ABC transporters is shown. The exposure of skin cells to UV radiation often leads to increased activity of ABC transporters-as has been observed in the case of MDRs, TAPs, CFTR, and BCRP. A different effect of oxidative stress has been observed in the case of mitochondrial SURs. However, the limited data in the literature-as indicated in this article-highlights the limited number of experimental studies dealing with the role of ABC transporters in the physiology and pathophysiology of skin cells and the skin as a whole. At the same time, the importance of such knowledge in relation to the possibility of daily exposure to UV radiation and xenobiotics, used for both skin care and the treatment of its diseases, is emphasized.

Protective effect of low-intensity treadmill exercise against acetylcholine-calcium chloride-induced atrial fibrillation in mice

Atrial fibrillation (AF) is the most common supraventricular arrhythmia, and it corresponds highly with exercise intensity. Here, we induced AF in mice using acetylcholine (ACh)-CaCl₂ for 7 days and aimed to determine the appropriate exercise intensity (no, low, moderate, high) to protect against AF by running the mice at different intensities for 4 weeks before the AF induction by ACh-CaCl₂. We examined the AF-induced atrial remodeling using electrocardiogram, patch-clamp, and immunohistochemistry. After the AF induction, heart rate, % increase of heart rate, and heart weight/body weight ratio were significantly higher in all the four AF groups than in the normal control; highest in the high-ex AF and lowest in the low-ex (lower than the no-ex AF), which indicates that low-ex treated the AF. Consistent with these changes, G protein-gated inwardly rectifying K⁺ currents, which were induced by ACh, increased in an exercise intensity-dependent manner and were lower in the low-ex AF than the no-ex AF. The peak level of Ca²⁺ current (at 0 mV) increased also in an exercise intensity-dependent manner and the inactivation time constants were shorter in all AF groups except for the low-ex AF group, in which the time constant was similar to that of the control. Finally, action potential duration was shorter in all the four AF groups than in the normal control; shortest in the high-ex AF and longest in the low-ex AF. Taken together, we conclude that low-intensity exercise protects the heart from AF, whereas high-intensity exercise might exacerbate AF.

ATP-sensitive potassium channels: A double-edged sword in neurodegenerative diseases

ATP-sensitive potassium channels (K_ATP channels), a group of vital channels that link the electrical activity of the cell membrane with cell metabolism, were discovered on the ventricular myocytes of guinea pigs by Noma using the patch-clamp technique in 1983. Subsequently, K_ATP channels have been found to be expressed in pancreatic β cells, cardiomyocytes, skeletal muscle cells, and nerve cells in the substantia nigra (SN), hippocampus, cortex, and basal ganglia. K_ATP channel openers (KCOs) diazoxide, nicorandil, minoxidil, and the K_ATP channel inhibitor glibenclamide have been shown to have anti-hypertensive, anti-myocardial ischemia, and insulin-releasing regulatory effects. Increasing evidence has suggested that K_ATP channels also play roles in Alzheimer's disease (AD), Parkinson's disease (PD), vascular dementia (VD), Huntington's disease (HD) and other neurodegenerative diseases. KCOs and K_ATP channel inhibitors protect neurons from injury by regulating neuronal excitability and neurotransmitter release, inhibiting abnormal protein aggregation and Ca²⁺ overload, reducing reactive oxygen species (ROS) production and microglia activation. However, K_ATP channels have dual effects in some cases. In this review, we focus on the roles of K_ATP channels and their related openers and inhibitors in neurodegenerative diseases. This will enable us to precisely take advantage of the K_ATP channels and provide new ideas for the treatment of neurodegenerative diseases.

The multifaceted role of cytochrome P450-Derived arachidonic acid metabolites in diabetes and diabetic cardiomyopathy

Understanding lipid metabolism is a critical key to understanding the pathogenesis of Diabetes Mellitus (DM). It is known that 60-90% of DM patients are obese or used to be obese. The incidence of obesity is rising owing to the modern sedentary lifestyle that leads to insulin resistance and increased levels of free fatty acids, predisposing tissues to utilize more lipids with less glucose uptake. However, the exact mechanism is not yet fully elucidated. Diabetic cardiomyopathy seems to be associated with these alterations in lipid metabolism. Arachidonic acid (AA) is an important fatty acid that is metabolized to several bioactive compounds by cyclooxygenases, lipoxygenases, and the more recently discovered, cytochrome P450 (P450) enzymes. P450 metabolizes AA to either epoxy-AA (EETs) or hydroxy-AA (HETEs). Studies showed that EETs could have cardioprotective effects and beneficial effects in reversing abnormalities in glucose and insulin homeostasis. Conversely, HETEs, most importantly 12-HETE and 20-HETE, were found to interfere with normal glucose and insulin homeostasis and thus, might be involved in diabetic cardiomyopathy. In this review, we highlight the role of P450-derived AA metabolites in the context of DM and diabetic cardiomyopathy and their potential use as a target for developing new treatments for DM and diabetic cardiomyopathy.

The role of sulfonylureas in the treatment of type 2 diabetes

INTRODUCTION

Type 2 diabetes (T2D) is increasingly prevalent and associated with increased risk for cardiovascular and renal disease. After lifestyle modification, metformin is usually the first-line pharmacotherapy and sulfonylureas are traditionally added after metformin failure. However, with newer glucose lowering drugs that may have less risk of hypoglycemia or that may reduce cardiovascular and renal events, the position of sulfonylureas is being reevaluated.

AREAS COVERED

In this article, the authors review relevant publications related to the use of sulfonylureas.

EXPERT OPINION

Sulfonylureas are potent glucose lowering drugs. The risk of hypoglycemia varies with different drugs within the class and can be minimized by using the safer drugs, possibly in lower doses. Cardiovascular events do not appear to be increased with some of the newer generation drugs. The durability of glycemic control also appears comparable to other newer agents. Sulfonylureas are the preferred treatment for some types of monogenic diabetes and selection of T2D patients who may have greater benefit from sulfonylureas based on certain phenotypes and genotypes is likely to be refined further by precision medicine. Sulfonylureas are inexpensive and readily available everywhere and they are still the most frequently used second-line treatment for T2D in many parts of the world.

Sulfonylurea Receptor 1 in Central Nervous System Injury: An Updated Review

Sulfonylurea receptor 1 (SUR1) is a member of the adenosine triphosphate (ATP)-binding cassette (ABC) protein superfamily, encoded by Abcc8, and is recognized as a key mediator of central nervous system (CNS) cellular swelling via the transient receptor potential melastatin 4 (TRPM4) channel. Discovered approximately 20 years ago, this channel is normally absent in the CNS but is transcriptionally upregulated after CNS injury. A comprehensive review on the pathophysiology and role of SUR1 in the CNS was published in 2012. Since then, the breadth and depth of understanding of the involvement of this channel in secondary injury has undergone exponential growth: SUR1-TRPM4 inhibition has been shown to decrease cerebral edema and hemorrhage progression in multiple preclinical models as well as in early clinical studies across a range of CNS diseases including ischemic stroke, traumatic brain injury, cardiac arrest, subarachnoid hemorrhage, spinal cord injury, intracerebral hemorrhage, multiple sclerosis, encephalitis, neuromalignancies, pain, liver failure, status epilepticus, retinopathies and HIV-associated neurocognitive disorder. Given these substantial developments, combined with the timeliness of ongoing clinical trials of SUR1 inhibition, now, another decade later, we review advances pertaining to SUR1-TRPM4 pathobiology in this spectrum of CNS disease—providing an overview of the journey from patch-clamp experiments to phase III trials.

Electrophysiological study of Arabidopsis ABCB4 and PIN2 auxin transporters: Evidence of auxin activation and interaction enhancing auxin selectivity

Polar auxin transport through plant tissue strictly requires polarly localized PIN proteins and uniformly distributed ABCB proteins. A functional synergy between the two types of membrane protein where their localizations overlap may create the degree of asymmetric auxin efflux required to produce polar auxin transport. We investigated this possibility by expressing ABCB4 and PIN2 in human embryonic kidney cells and measuring whole-cell ionic currents with the patch-clamp technique and CsCl-based electrolytes. ABCB4 activity was 1.81-fold more selective for Cl- over Cs+ and for PIN2 the value was 2.95. We imposed auxin gradients and determined that ABCB4 and PIN2 were 12-fold more permeable to the auxin anion (IAA-) than Cl-. This measure of the intrinsic selectivity of the transport pathway was 21-fold when ABCB4 and PIN2 were co-expressed. If this increase occurs in plants, it could explain why asymmetric PIN localization is not sufficient to create polar auxin flow. Some form of co-action or synergy between ABCB4 and PIN2 that increases IAA- selectivity at the cell face where both occur may be important. We also found that auxin stimulated ABCB4 activity, which may contribute to a self-reinforcement of auxin transport known as canalization.

Envisioning the role of inwardly rectifying potassium (Kir) channel in epilepsy

Epilepsy is a devastating neurological disorder characterized by recurrent seizures attributed to the disruption of the dynamic excitatory and inhibitory balance in the brain. Epilepsy has emerged as a global health concern affecting about 70 million people worldwide. Despite recent advances in pre-clinical and clinical research, its etiopathogenesis remains obscure, and there are still no treatment strategies modifying disease progression. Although the precise molecular mechanisms underlying epileptogenesis have not been clarified yet, the role of ion channels as regulators of cellular excitability has increasingly gained attention. In this regard, emerging evidence highlights the potential implication of inwardly rectifying potassium (Kir) channels in epileptogenesis. Kir channels consist of seven different subfamilies (Kir1-Kir7), and they are highly expressed in both neuronal and glial cells in the central nervous system. These channels control the cell volume and excitability. In this review, we discuss preclinical and clinical evidence on the role of the several subfamilies of Kir channels in epileptogenesis, aiming to shed more light on the pathogenesis of this disorder and pave the way for future novel therapeutic approaches.

Role of Glucose-Lowering Medications in Erectile Dysfunction

Erectile dysfunction (ED) is a long-term complication of type 2 diabetes (T2D) widely known to affect the quality of life. Several aspects of altered metabolism in individuals with T2D may help to compromise the penile vasculature structure and functions, thus exacerbating the imbalance between smooth muscle contractility and relaxation. Among these, advanced glycation end-products and reactive oxygen species derived from a hyperglycaemic state are known to accelerate endothelial dysfunction by lowering nitric oxide bioavailability, the essential stimulus of relaxation. Although several studies have explained the pathogenetic mechanisms involved in the generation of erectile failure, few studies to date have described the efficacy of glucose-lowering medications in the restoration of normal sexual activity. Herein, we will present current knowledge about the main starters of the pathophysiology of diabetic ED and explore the role of different anti-diabetes therapies in the potential remission of ED, highlighting specific pathways whose activation or inhibition could be fundamental for sexual care in a diabetes setting.

The Ion Channel and GPCR Toolkit of Brain Capillary Pericytes

Brain pericytes reside on the abluminal surface of capillaries, and their processes cover ~90% of the length of the capillary bed. These cells were first described almost 150 years ago (Eberth, 1871; Rouget, 1873) and have been the subject of intense experimental scrutiny in recent years, but their physiological roles remain uncertain and little is known of the complement of signaling elements that they employ to carry out their functions. In this review, we synthesize functional data with single-cell RNAseq screens to explore the ion channel and G protein-coupled receptor (GPCR) toolkit of mesh and thin-strand pericytes of the brain, with the aim of providing a framework for deeper explorations of the molecular mechanisms that govern pericyte physiology. We argue that their complement of channels and receptors ideally positions capillary pericytes to play a central role in adapting blood flow to meet the challenge of satisfying neuronal energy requirements from deep within the capillary bed, by enabling dynamic regulation of their membrane potential to influence the electrical output of the cell. In particular, we outline how genetic and functional evidence suggest an important role for G_s-coupled GPCRs and ATP-sensitive potassium (K_ATP) channels in this context. We put forth a predictive model for long-range hyperpolarizing electrical signaling from pericytes to upstream arterioles, and detail the TRP and Ca²⁺ channels and G_q, G_i/o, and G_12/13 signaling processes that counterbalance this. We underscore critical questions that need to be addressed to further advance our understanding of the signaling topology of capillary pericytes, and how this contributes to their physiological roles and their dysfunction in disease.

Embryonic cardioprotection by hydrogen sulphide: studies of isolated cardiac function and ischaemia-reperfusion injury in the chicken embryo

KEY POINTS

In mammals, pregnancy complications can trigger an embryonic or fetal origin of cardiac dysfunction. However, underlying mechanisms remain uncertain because the partial contributions of the challenge on the mother, placenta or offspring are difficult to disentangle. The avian embryo permits isolation of the direct effects of suboptimal conditions during development on the cardiac function of the offspring, independent of additional effects on the mother and/or the placenta. Therefore, the objectives of this work were to adapt the isolated Langendorff technique using the chicken embryo to study the physiology of the developing heart. Here, we introduce a novel technique and show the utility of the technique for exploring cardioprotective roles of H₂ S in the chicken embryo heart. This work lays the foundation for studying the direct effects of H₂ S therapy on the embryonic heart independent of effects on the mother and the placenta in adverse development.

ABSTRACT

This study adapted the isolated Langendorff preparation to study the chicken embryo heart in response to ischaemia-reperfusion (IR) injury. The utility of the technique was tested by investigating cardioprotective effects of hydrogen sulphide (H₂ S) and underlying mechanisms. Embryonic hearts (19 out of 21 days of incubation) mounted on a Langendorff preparation were exposed to IR (30 min ischaemia) after 4 treatments administered randomly, all as a 1 mm bolus, into the perfusate: saline vehicle (control); sodium hydrogen sulphide (NaHS); NaHS plus glibenclamide, an antagonist of K_ATP opening (NaHS Glib), and Glib alone (Glib). Relative to controls, NaHS treatment improved cardiac function after ischaemia (mean ± SD for area under the curve, AUC, for left ventricular developed pressure, LVDP: 1767.3 ± 929.5 vs. 492.7 ± 308.1; myocardial contractility, dP/dt_max : 2748.9 ± 1514.9 vs. 763.7 ± 433.1) and decreased infarct size (22.7 ± 8.0 vs. 43.9 ± 4.2%) and cardiac damage (% change in creatinine kinase, 49.3 ± 41.3 vs. 214.6 ± 155.1; all P < 0.05). Beneficial effects of NaHS were blocked by Glib. Glib alone had no effects. NaHS increased coronary flow rate (CFR) during baseline (mean ± SD for AUC: 134.3 ± 91.6 vs. 92.2 ± 35.8) and post IR (1467 ± 529.5 vs. 748.0 ± 222.1; both P < 0.05). However, this effect was not prevented by Glib. Therefore, the chicken embryo heart is amenable for study via the Langendorff preparation under basal conditions and during IR. The data show that H₂ S confers embryonic cardiac protection via opening of myocardial K_ATP channels and not via increasing CFR. H₂ S may prove a useful therapeutic agent to protect the human fetal heart against IR injury, as may occur in complicated labour.

Metabolic regulation of endothelial SK channels and human coronary microvascular function

BACKGROUND

Diabetic (DM) inactivation of small conductance calcium-activated potassium (SK) channels contributes to coronary endothelial dysfunction. However, the mechanisms responsible for this down-regulation of endothelial SK channels are poorly understood. Thus, we hypothesized that the altered metabolic signaling in diabetes regulates endothelial SK channels and human coronary microvascular function.

METHODS

Human atrial tissue, coronary arterioles and coronary artery endothelial cells (HCAECs) obtained from DM and non-diabetic (ND) patients (n = 12/group) undergoing cardiac surgery were used to analyze metabolic alterations, endothelial SK channel function, coronary microvascular reactivity and SK gene/protein expression/localization.

RESULTS

The relaxation response of DM coronary arterioles to the selective SK channel activator SKA-31 and calcium ionophore A23187 was significantly decreased compared to that of ND arterioles (p < 0.05). Diabetes increases the level of NADH and the NADH/NAD+ ratio in human myocardium and HCAECs (p < 0.05). Increase in intracellular NADH (100 μM) in the HCAECs caused a significant decrease in endothelial SK channel currents (p < 0.05), whereas, intracellular application of NAD+ (500 μM) increased the endothelial SK channel currents (p < 0.05). Mitochondrial reactive oxygen species (mROS) of HCAECs and NADPH oxidase (NOX) and PKC protein expression in the human myocardium and coronary microvasculature were increased respectively (p < 0.05).

CONCLUSIONS

Diabetes is associated with metabolic changes in the human myocardium, coronary microvasculature and HCAECs. Endothelial SK channel function is regulated by the metabolite pyridine nucleotides, NADH and NAD+, suggesting that metabolic regulation of endothelial SK channels may contribute to coronary endothelial dysfunction in the DM patients with diabetes.

Pleiotropic effects of anti-diabetic drugs: A comprehensive review

Diabetes mellitus characterized by hyperglycaemia presents an array of comorbidities such as cardiovascular and renal failure, dyslipidemia, and cognitive impairments. Populations above the age of 60 are in an urgent need of effective therapies to deal with the complications associated with diabetes mellitus. Widely used anti-diabetic drugs have good safety profiles and multiple reports indicate their pleiotropic effects in diabetic patients or models. This review has been written with the objective of identifying the widely-marketed anti-diabetic drugs which can be efficiently repurposed for the treatment of other diseases or disorders. It is an updated, comprehensive review, describing the protective role of various classes of anti-diabetic drugs in mitigating the macro and micro vascular complications of diabetes mellitus, and differentiating these drugs on the basis of their mode of action. Notably, metformin, the anti-diabetic drug most commonly explored for cancer therapy, has also exhibited some antimicrobial effects. Unlike class specific effects, few instances of drug specific effects in managing cardiovascular complications have also been reported. A major drawback is that the pleiotropic effects of anti-diabetic drugs have been mostly investigated only in diabetic patients. Thus, for effective repurposing, more clinical trials devoted to analyse the effects of anti-diabetic drugs in patients irrespective of their diabetic condition, are required.

Toxicity of Metformin and Hypoglycemic Therapies

Metformin along with other antidiabetic medications provide benefit to patients in the treatment of type 2 diabetes mellitus, but caution is advised in certain scenarios to avoid toxicity in kidney disease. Renal dosing, monitoring of kidney function, and evaluating the risk of developing serious side effects are warranted with some agents. The available literature with regard to incidence of adverse events and toxicity of hypoglycemic therapies is reviewed.

The right place for Sulphonylureas today

The place of Sulphonylurea based insulin secretagogues in the management of Type 2 diabetes appears as controversial today as it was fifty years ago. Newer therapies are associated with less hypoglycaemia and weight gain than Sulphonylureas but currently cost more and lack assurances which come with long-term exposure. Emergence of recent CVOT data for SGLT-2 inhibitors and GLP-1 receptor agonists is likely to influence therapeutic choices and guidance is now supportive of their earlier use in cases at high risk of cardiovascular disease. Meta-analyses of Sulphonylurea trials have failed to indicate a consistent effect (positive or negative) on cardiovascular disease or mortality, although are limited by the relative scarcity of studies directly reporting these outcomes. The CAROLINA trial is reassuring in demonstrating cardiovascular safety for the Sulphonylurea Glimepiride when compared directly with the DPP-4 inhibitor Linagliptin, suggesting either of these agents would be relatively safe second line options after Metformin in the majority of patients. This review provides a balanced assessment of available Sulphonylurea treatments in the context of current cardiovascular outcome trial data (CVOT) data and hopefully assists informed decision making about the place of these drugs in contemporary glucose lowering practice.

A Variation in the ABCC8 Gene Is Associated with Type 2 Diabetes Mellitus and Repaglinide Efficacy in Chinese Type 2 Diabetes Mellitus Patients

Objective Previous studies have suggested that variations in the ABCC8 gene may be closely associated with T2DM susceptibility and repaglinide response. However, these results have not been entirely consistent, and there are no related studies in a Chinese population, suggesting the need for further exploration. The current study investigated the associations of the ABCC8 rs1801261 polymorphism with type 2 diabetes mellitus (T2DM) susceptibility and repaglinide therapeutic efficacy in Chinese Han T2DM patients. Methods A total of 234 T2DM patients and 105 healthy subjects were genotyped for ABCC8 rs1801261 polymorphism by a polymerase chain reaction-restriction fragment length polymorphism assay. A total of 70 patients with the same genotypes of CYP2C8*3 139Arg and OATP1B1 521TT were randomized to orally take 3 mg repaglinide per day (1 mg each time before meals) for 8 consecutive weeks. The pharmacodynamic parameters of repaglinide and biochemical indicators were then determined before and after repaglinide treatment. Results The frequency of ABCC8 rs1801261 allele was higher in T2DM patients than in the control subjects (22.6% vs.11.0%, p<0.01). After repaglinide treatment, T2DM patients carrying genotype CT showed a significantly attenuated efficacy on FPG (p<0.01) and HbA1c (p<0.01) compared with those with genotype CC. Conclusion These results suggested that the ABCC8 rs1801261 polymorphism might influence T2DM susceptibility and the therapeutic effect of repaglinide in Chinese Han T2DM patients. This study was registered in the Chinese Clinical Trial Register on May 14, 2013 (No. ChiCTR-CCC13003536).

Sulfonylurea derivatives and cancer, friend or foe?

Type 2 diabetes mellitus (T2DM) is associated with a higher risk of cancer and cancer-related mortality. Increased blood glucose and insulin levels in T2DM patients may be, at least in part, responsible for this effect. Indeed, lowering glucose and/or insulin levels pharmacologically appears to reduce cancer risk and progression, as has been demonstrated for the biguanide metformin in observational studies. Studies investigating the influence of sulfonylurea derivatives (SUs) on cancer risk have provided conflicting results, partly due to comparisons with metformin. Furthermore, little attention has been paid to within-class differences in systemic and off-target effects of the SUs. The aim of this systematic review is to discuss the available preclinical and clinical evidence on how the different SUs influence cancer development and risk. Databases including PubMed, Cochrane, Database of Abstracts on Reviews and Effectiveness, and trial registries were systematically searched for available clinical and preclinical evidence on within-class differences of SUs and cancer risk. The overall preclinical and clinical evidence suggest that the influence of SUs on cancer risk in T2DM patients differs between the various SUs. Potential mechanisms include differing affinities for the sulfonylurea receptors and thus differential systemic insulin exposure and off-target anti-cancer effects mediated for example through potassium transporters and drug export pumps. Preclinical evidence supports potential anti-cancer effects of SUs, which are of interest for further studies and potentially repurposing of SUs. At this time, the evidence on differences in cancer risk between SUs is not strong enough to guide clinical decision making.

Emerging roles for multifunctional ion channel auxiliary subunits in cancer

Several superfamilies of plasma membrane channels which regulate transmembrane ion flux have also been shown to regulate a multitude of cellular processes, including proliferation and migration. Ion channels are typically multimeric complexes consisting of conducting subunits and auxiliary, non-conducting subunits. Auxiliary subunits modulate the function of conducting subunits and have putative non-conducting roles, further expanding the repertoire of cellular processes governed by ion channel complexes to processes such as transcellular adhesion and gene transcription. Given this expansive influence of ion channels on cellular behaviour it is perhaps no surprise that aberrant ion channel expression is a common occurrence in cancer. This review will focus on the conducting and non-conducting roles of the auxiliary subunits of various Ca2+, K+, Na+ and Cl- channels and the burgeoning evidence linking such auxiliary subunits to cancer. Several subunits are upregulated (e.g. Cavβ, Cavγ) and downregulated (e.g. Kvβ) in cancer, while other subunits have been functionally implicated as oncogenes (e.g. Navβ1, Cavα2δ1) and tumour suppressor genes (e.g. CLCA2, KCNE2, BKγ1) based on in vivo studies. The strengthening link between ion channel auxiliary subunits and cancer has exposed these subunits as potential biomarkers and therapeutic targets. However further mechanistic understanding is required into how these subunits contribute to tumour progression before their therapeutic potential can be fully realised.

Diabesity and antidiabetic drugs

The prevalence of "diabesity" - diabetes related to obesity - has increased tremendously over the past few decades because of the global obesity epidemic. Although bariatric surgery is the best treatment option for patients with diabesity, a majority of patients are managed only with antidiabetic drugs for various reasons. Diabetes control with antidiabetic agents may affect diabesity outcomes positively or negatively because of their effects on body weight and other metabolic parameters. For this reason, rational use of anti-diabetic medications is imperative to optimise long-term management of diabesity. Understanding the molecular mechanisms of antidiabetic drugs and/or drug combinations on diabesity outcomes are therefore important not only for the basic scientists but also for clinicians. This review explores the molecular signalling cascades of antidiabetic medications in the management of diabesity.

2,2-Dimethyl-3,4-dihydro-2H-1,4-benzoxazines as isosteres of 2,2-dimethylchromans acting as inhibitors of insulin release and vascular smooth muscle relaxants

The present study describes the synthesis and biological evaluation of 4-phenylureido/thioureido-substituted 2,2-dimethyl-3,4-dihydro-2H-1,4-benzoxazines as isosteres of corresponding 2,2-dimethylchromans reported to be pancreatic β-cell K_ATP channel openers. The benzoxazines were found to be less active as inhibitors of the glucose-induced insulin release than their corresponding chromans, while the myorelaxant activity of some 4-arylureido-substituted benzoxazines was more pronounced than that exhibited by their chroman counterparts. The myorelaxant activity of the most potent benzoxazine 8e was further characterized on rat aortic rings precontracted by 30 mM KCl in the presence of glibenclamide (10 μM) or precontracted by 80 mM extracellular KCl. Our findings indicate that, on vascular smooth muscle cells, the benzoxazine 8e mainly behaved as a calcium entry blocker.

Ability of CP-532,903 to protect mouse hearts from ischemia/reperfusion injury is dependent on expression of A3 adenosine receptors in cardiomyoyctes

A₃ adenosine receptor (A₃AR) agonists are effective at limiting injury caused by ischemia/reperfusion injury of the heart in experimental animal models. However, understanding of their mechanism of action, which is likely multifactorial, remains incomplete. In prior studies, it has been demonstrated that A₃AR-mediated ischemic protection is blocked by glibenclamide and is absent in Kir6.2 gene ablated mice that lack the pore-forming subunit of the ATP-sensitive potassium (K_ATP) channel, suggesting one contributing mechanism may involve accelerated activation of K_ATP channels. However, presence of A₃ARs in the myocardium has yet to be established. Utilizing a whole-cell recording technique, in this study we confirm functional expression of the A₃AR in adult mouse ventricular cardiomyocytes, coupled to activation of ATP-dependent potassium (K_ATP) channels via G_i inhibitory proteins. We further show that ischemic protection provided by the selective A₃AR agonist CP-532,903 in an isolated, buffer-perfused heart model is lost completely in Adora3^{LoxP/LoxP;Myh6-Cre} mice, which is a newly developed model developed and comprehensively described herein whereby the A₃AR gene (Adora3) is deleted exclusively in cardiomyocytes. Our findings, taken together with previously published work, are consistent with the hypothesis that A₃AR agonists provide ischemic tolerance, at least in part, by facilitating opening of myocardial K_ATP channels.

Do sulphonylureas still have a place in clinical practice?

Sulphonylureas have been commercially available since the 1950s, but their use continues to be associated with controversy. Although adverse cardiovascular outcomes in some observational studies have raised concerns about sulphonylureas, findings from relatively recent, robust, and high-quality systematic reviews have indicated no increased risk of all-cause mortality associated with sulphonylureas compared with other active treatments. Results from large, multicentre, randomised controlled trials such as the UK Prospective Diabetes Study and ADVANCE have confirmed the microvascular benefits of sulphonylureas, a reduction in the incidence or worsening of nephropathy and retinopathy, and no increase in all-cause mortality, although whether these benefits were due to sulphonylurea therapy and not an overall glucose-lowering effect could not be confirmed. A comparison of sulphonylureas and pioglitazone in the TOSCA.IT trial also confirmed the efficacy and cardiovascular safety of sulphonylureas. Investigators of randomised controlled trials have reported an increased risk of hypoglycaemia and weight gain with sulphonylureas, but data from observational studies suggest that the incidence of severe hypoglycaemia is lower in people taking sulphonylurea than in people taking insulin, and weight gain with sulphonylureas has been relatively modest in large cohort studies. 80% of people with diabetes live in low-to-middle income countries, so the effectiveness, affordability, and safety of sulphonylureas are particularly important considerations when prescribing glucose-lowering therapy. Results of ongoing head-to-head studies with new drugs, such as the comparison of glimepiride with linagliptin in the CAROLINA study and the comparison of various therapies (including sulphonylureas) for glycaemic control in the GRADE study, will determine the place of sulphonylureas in glucose-lowering therapy algorithms for patients with type 2 diabetes.

Sulfonylurea and neuroprotection: The bright side of the moon

Sulfonylurea (SUR) agents are the second and most used oral hypoglycemic drugs after metformin and they still as an imperative tool for most favorable of glucose control. SURs are used mainly in the management of Type 2 diabetes mellitus since; they are effective in the glycemic control and reduction of microvascular complications. First-generation SUR represents 3% of used oral hypoglycemic agents while second and third generations are used in about 25% in patients with Type 2 diabetes mellitus. Upregulation of SUR1 receptor has been observed after stroke and traumatic brain injury, therefore, SUR such as glibenclamide inhibits brain edema and astrocyte swelling following brain insults. SUR drugs mainly glibenclamide is effective at a low dose in the management of cerebral stroke and could be a contestant with corticosteroid in controlling brain edema.

Insulin down-regulates cardioprotective SUR2A in the heart-derived H9c2 cells: A possible explanation for some adverse effects of insulin therapy

Some recent studies associated insulin therapy with negative cardiovascular events and shorter lifespan. SUR2A, a K_ATP channel subunit, regulate cardioprotection and cardiac ageing. Here, we have tested whether glucose and insulin regulate expression of SUR2A/K_ATP channel subunits and resistance to metabolic stress in heart H9c2 cells. Absence of glucose in culture media decreased SUR2A mRNA, while mRNAs of Kir6.2, Kir6.1, SUR1 and IES SUR2B were increased. 2-deoxyglucose (50 mM) decreased mRNAs of SUR2A, SUR2B and SUR1, did not affect IES SUR2A and IES SUR2B mRNAs and increased Kir6.2 mRNA. No glucose and 2-deoxyglucose (50 mM) decreased resistance to an inhibitor of oxidative phosphorylation, DNP (10 mM). 50 mM glucose did not alter K_ATP channel subunits nor cellular resistance to DNP (10 mM). Insulin (20 ng/ml) in both physiological and high glucose (50 mM) down-regulated SUR2A while upregulating Kir6.1 and Kir6.2 (in high glucose only). Insulin (20 ng/ml) in physiological and high glucose decreased cell survival in DNP (10 mM). As opposed to Kir6.2, infection with SUR2A resulted in titre-dependent cytoprotection. We conclude that insulin decreases resistance to metabolic stress in H9c2 cells by decreasing SUR2A expression. Lower cardiac SUR2A levels underlie increased myocardial susceptibility to metabolic stress and shorter lifespan.

Profile of intravenous glyburide for the prevention of cerebral edema following large hemispheric infarction: evidence to date

Glyburide (also known as glibenclamide) is a second-generation sulfonylurea drug that inhibits sulfonylurea receptor 1 (Sur1) at nanomolar concentrations. Long used to target K_ATP (Sur1–Kir6.2) channels for the treatment of diabetes mellitus type 2, glyburide was recently repurposed to target Sur1–transient receptor potential melastatin 4 (Trpm4) channels in acute central nervous system injury. Discovered nearly two decades ago, SUR1–TRPM4 has emerged as a critical target in stroke, specifically in large hemispheric infarction, which is characterized by edema formation and life-threatening brain swelling. Following ischemia, SUR1–TRPM4 channels are transcriptionally upregulated in all cells of the neurovascular unit, including neurons, astrocytes, microglia, oligodendrocytes and microvascular endothelial cells. Work by several independent laboratories has linked SUR1–TRPM4 to edema formation, with blockade by glyburide reducing brain swelling and death in preclinical models. Recent work showed that, following ischemia, SUR1–TRPM4 co-assembles with aquaporin-4 to mediate cellular swelling of astrocytes, which contributes to brain swelling. Additionally, recent work linked SUR1–TRPM4 to secretion of matrix metalloproteinase-9 (MMP-9) induced by recombinant tissue plasminogen activator in activated brain endothelial cells, with blockade of SUR1–TRPM4 by glyburide reducing MMP-9 and hemorrhagic transformation in preclinical models with recombinant tissue plasminogen activator. The recently completed GAMES (Glyburide Advantage in Malignant Edema and Stroke) clinical trials on patients with large hemispheric infarctions treated with intravenous glyburide (RP-1127) revealed promising findings with regard to brain swelling (midline shift), MMP-9, functional outcomes and mortality. Here, we review key elements of the basic science, preclinical experiments and clinical studies, both retrospective and prospective, on glyburide in focal cerebral ischemia and stroke.

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.

Antidiabetic therapies and male reproductive function: where do we stand?

Diabetes mellitus has been increasing at alarming rates in recent years, thus jeopardizing human health worldwide. Several antidiabetic drugs have been introduced in the market to manage glycemic levels, and proven effective in avoiding, minimizing or preventing the appearance or development of diabetes mellitus-related complications. However, and despite the established association between such pathology and male reproductive dysfunction, the influence of these therapeutic interventions on such topics have been scarcely explored. Importantly, this pathology may contribute toward the global decline in male fertility, giving the increasing preponderance of diabetes mellitus in young men at their reproductive age. Therefore, it is mandatory that the reproductive health of diabetic individuals is maintained during the antidiabetic treatment. With this in mind, we have gathered the available information and made a critical analysis regarding the effects of several antidiabetic drugs on male reproductive function. Unlike insulin, which has a clear and fundamental role on male reproductive function, the other antidiabetic therapies' effects at this level seem incoherent. In fact, studies are highly controversial possibly due to the different experimental study approaches, which, in our opinion, suggests caution when it comes to prescribing such drugs to young diabetic patients. Overall, much is still to be determined and further studies are needed to clarify the safety of these antidiabetic strategies on male reproductive system. Aspects such as the effects of insulin levels variations, consequent of insulin therapy, as well as what will be the impact of the side effect hypoglycemia, common to several therapeutic strategies discussed, on the male reproductive system are still to be addressed.

Repair of UV-Induced DNA Damage Independent of Nucleotide Excision Repair Is Masked by MUTYH

DNA lesions caused by UV damage are thought to be repaired solely by the nucleotide excision repair (NER) pathway in human cells. Patients carrying mutations within genes functioning in this pathway display a range of pathologies, including an increased susceptibility to cancer, premature aging, and neurological defects. There are currently no curative therapies available. Here we performed a high-throughput chemical screen for agents that could alleviate the cellular sensitivity of NER-deficient cells to UV-induced DNA damage. This led to the identification of the clinically approved anti-diabetic drug acetohexamide, which promoted clearance of UV-induced DNA damage without the accumulation of chromosomal aberrations, hence promoting cellular survival. Acetohexamide exerted this protective function by antagonizing expression of the DNA glycosylase, MUTYH. Together, our data reveal the existence of an NER-independent mechanism to remove UV-induced DNA damage and prevent cell death.

The Infamous, Famous Sulfonylureas and Cardiovascular Safety: Much Ado About Nothing?

PURPOSE OF REVIEW

Sulfonylureas (SUs) are one of the most commonly used glucose-lowering agents worldwide. While their efficacy is undisputed, their cardiovascular safety has been debated since the 1970's.

RECENT FINDINGS

With no dedicated cardiovascular studies to definitively answer this question, observational studies and meta-analyses abound and have reported divergent results, fueling the controversy. Studies that compared SUs to metformin or newer agents, like GLP-1 agonists and SGLT2 inhibitors, suggest a difference in cardiovascular events, yet this is likely the result of beneficial effects of the latter. Studies comparing SUs to other agents have been reassuring. SUs remain a common choice of treatment for patients with type 2 diabetes due to their exceptional value. They are effective at lowering glucose and thus contributing to the prevention of microvascular complications. Weight gain and hypoglycemia are their main side effects, although less severe when compared to insulin treatment. Their cardiovascular safety will remain a controversial topic due to lack of conclusive data, but there is no definitive evidence of harm with the second-generation agents.

Calcium dynamics control K-ATP channel-mediated bursting in substantia nigra dopamine neurons: a combined experimental and modeling study

Burst firing in medial substantia nigra (mSN) dopamine (DA) neurons has been selectively linked to novelty-induced exploration behavior in mice. Burst firing in mSN DA neurons, in contrast to lateral SN DA neurons, requires functional ATP-sensitive potassium (K-ATP) channels both in vitro and in vivo. However, the precise role of K-ATP channels in promoting burst firing is unknown. We show experimentally that L-type calcium channel activity in mSN DA neurons enhances open probability of K-ATP channels. We then generate a mathematical model to study the role of Ca²⁺ dynamics driving K-ATP channel function in mSN DA neurons during bursting. In our model, Ca²⁺ influx leads to local accumulation of ADP due to Ca-ATPase activity, which in turn activates K-ATP channels. If K-ATP channel activation reaches levels sufficient to terminate spiking, rhythmic bursting occurs. The model explains the experimental observation that, in vitro, coapplication of NMDA and a selective K-ATP channel opener, NN414, is required to elicit bursting as follows. Simulated NMDA receptor activation increases the firing rate and the rate of Ca²⁺ influx, which increases the activation of K-ATP. The model suggests that additional sources of hyperpolarization, such as GABAergic synaptic input, are recruited in vivo for burst termination or rebound burst discharge. The model predicts that NN414 increases the sensitivity of the K-ATP channel to ADP, promoting burst firing in vitro, and that that high levels of Ca²⁺ buffering, as might be expected in the calbindin-positive SN DA neuron subpopulation, promote rhythmic bursting pattern, consistent with experimental observations in vivo. NEW & NOTEWORTHY Recently identified distinct subpopulations of midbrain dopamine neurons exhibit differences in their two primary activity patterns in vivo: tonic (single spike) firing and phasic bursting. This study elucidates the biophysical basis of bursts specific to dopamine neurons in the medial substantia nigra, enabled by ATP-sensitive K⁺ channels and necessary for novelty-induced exploration. A better understanding of how dopaminergic signaling differs between subpopulations may lead to therapeutic strategies selectively targeted to specific subpopulations.

KATP channels in high glucose-induced rat mesangial cell proliferation and release of MMP-2 and fibronectin

ATP-sensitive potassium (KATP) channels are well characterized in cardiac, pancreatic and many other muscle cells. The purpose of this study was to determine if KATP channels play a role in diabetic nephropathy (DN). In the present study, functional expression of the KATP channel was examined in rat mesangial cells with or without high glucose (HG) stimulation. The mesangial cell proliferation and the release of matrix metalloproteinase (MMP)-2 and fibronectin in response to high glucose with a selective opener of KATP (diazoxide, DZX), or with a selective inhibitor of KATP (5-hydroxydecanoate, 5-HD) were also measured. The cell proliferation was observed using Cell Counting Kit-8 assay, and the mRNA expressions of KATP subunit, including Kir6.1, Kir6.2, sulfonylurea receptor 1 (SUR1), SUR2A and SUR2B, were assessed using quantitative real-time PCR. MMP-2 and fibronectin release was measured by ELISA. The present study clarified expression of SUR subunit of KATP in plasma. HG treatment could cause increased cell proliferation and release of MMP-2 and fibronectin in a dose-dependent manner. HG also significantly decreased the expression of Kir6.1, SUR2A and SUR2B. Pretreatment of DZX markedly decreased the expression of SUR1, SUR2A and SUR2B, but had no effect on Kir6.1 expression compared with HG alone, while these changes were inhibited by 5-HD pretreatment. Moreover, DZX also inhibited cell proliferation and release of MMP-2 and fibronectin in HG-induced rat mesangial cells, and that was corrected by 5-HD. These data suggest that HG stimulates mesangial cell proliferation and cellular matrix release via inhibiting KATP channel activity, leading us to propose that KATP channel dysfunction may be involved in the development of DN.

Cardiac Effects of Sulfonylurea-Related Hypoglycemia

OBJECTIVE

To determine the effect of sulfonylurea-related hypoglycemia on cardiac repolarization and ectopy in the setting of well-controlled type 2 diabetes.

RESEARCH DESIGN AND METHODS

Thirty subjects with sulfonylurea-treated type 2 diabetes underwent 48 h of concurrent continuous glucose monitoring and ambulatory electrocardiography. Ventricular repolarization (QTc) and QT dynamicity were analyzed during periods of hypoglycemia (<3.5 mmol/L for >20 min) and compared with periods of euglycemia and hyperglycemia combined. Cardiac ectopy rates during hypoglycemia were compared with ectopy rates when blood glucose was 4-10 mmol/L.

RESULTS

Mean HbA_1c was 6.9% (52 mmol/mol). Hypoglycemia was detected in 9 of 30 subjects (30%); episodes were typically nocturnal (67%) and asymptomatic (73%). Hypoglycemia-associated QTc prolongation was seen in five of nine subjects with a large variation in individual response. Higher QT dynamicity, a poor prognostic factor in cardiac disease, was seen in subjects who experienced hypoglycemia compared with subjects who did not (0.193 vs. 0.159 for the nocturnal period; P = 0.01). This finding persisted after the hypoglycemic event. The rates of ventricular and supraventricular ectopy demonstrated a nonsignificant trend toward an increase during hypoglycemia (median rate ratio 1.58 and 1.33, respectively). Similar, nonsignificant results were observed in a separate insulin-treated cohort.

CONCLUSIONS

Hypoglycemia, often unrecognized, is a frequent finding in well-controlled sulfonylurea-treated type 2 diabetes. It is associated with the novel finding of increased QT dynamicity and QTc prolongation in some individuals. Our findings suggest sulfonylurea-related hypoglycemia can have detrimental cardiovascular sequelae. Similar effects are also seen in the setting of insulin therapy.

Opening of the Adenosine Triphosphate-sensitive Potassium Channel Attenuates Morphine Tolerance by Inhibiting JNK and Astrocyte Activation in the Spinal Cord

OBJECTIVES

In the present study, we investigated the role of adenosine triphosphate (ATP)-sensitive potassium (KATP) channels in chronic morphine tolerance.

MATERIALS AND METHODS

Male mice were injected intrathecally with morphine or saline, respectively (each in 10 μL). Different doses of the KATP opener cromakalim (0.3, 1, or 3 μg/10 μL/mouse) were administered 15 minutes before the morphine (10 μg/10 μL/mouse) challenge daily for 7 consecutive days. Half an hour after morphine injection, the tail-flick latency was measured to evaluate the antinociceptive effect of morphine. On the seventh day, mice were euthanized with sodium pentobarbital (100 mg/kg) at 1 hour after morphine injection, and their spinal cords were removed for the assays of Western blot, immunofluorescence, and quantitative real-time polymerase chain reaction.

RESULTS

Opening of the KATP channel attenuates chronic morphine tolerance, suppresses astrocyte activation inhibits the increase in interleukin-1β at the transcriptional and the translational levels, and reduces the upregulation of phosphorylated c-Jun N-terminal kinase mitogen-activated protein kinase in the spinal cord after chronic morphine treatment. Moreover, transcriptional levels of spinal cord astrocyte KATP channel subunits, named the inwardly rectifying potassium (Kir) 6.1 and sulfonylurea receptor 1, are decreased in morphine-tolerant mice.

DISCUSSION

Cromakalim suppresses morphine-induced astrocyte activation significantly by suppressing the c-Jun N-terminal kinase pathway, resulting in a reduced release of interleukin-1β and the attenuation of morphine chronic antinociceptive tolerance.

Exposure to 15% oxygen in vivo up-regulates cardioprotective SUR2A without affecting ERK1/2 and AKT: a crucial role for AMPK

SUR2A is an 'atypical' ABC protein that forms sarcolemmal ATP-sensitive K⁺ (K_ATP ) channels by binding to inward rectifier Kir6.2. Manipulation with SUR2A levels has been suggested to be a promising therapeutic strategy against ischaemic heart diseases and other diseases where increased heart resistance to stress is beneficial. Some years ago, it has been reported that high-altitude residents have lower mortality rates for ischaemic heart disease. The purpose of this study was to determine whether SUR2A is regulated by mild-to-severe hypoxic conditions (15% oxygen; oxygen tension equivalent to 3000 m above sea level) and elucidate the underlying mechanism. Mice were exposed to either to 21% (control) or 15% concentration of oxygen for 24 hrs. Twenty-four hours long exposure to 15% oxygen decreased partial pressure of O2 (PO₂ ), but did not affect blood CO₂ (PCO₂ ), haematocrit nor levels of ATP, lactate and NAD+/NADH in the heart. Cardiac SUR2A levels were significantly increased while Kir6.2 levels were not affected. Hypoxia did not induce phosphorylation of extracellular signal-regulated kinases (ERK1/2) or protein kinase B (Akt), but triggered phosphorylation of AMP activated protein kinase (AMPK). AICAR, an activator of AMPK, increased the level of SUR2A in H9c2 cells. We conclude that oxygen increases SUR2A level by activating AMPK. This is the first account of AMPK-mediated regulation of SUR2A.

CD200 Inhibits Inflammatory Response by Promoting KATP Channel Opening in Microglia Cells in Parkinson's Disease

Background

As the second most common neurodegenerative disorder after Alzheimer’s disease (AD), Parkinson’s disease (PD) principally impacts the motor system in approximately 7 million patients worldwide. The present study aimed to explore the effects of cluster of differentiation (CD200) on adenosine triphosphate-sensitive potassium (KATP) channels and inflammatory response in PD mice.

Material/Methods

We created an in vivo PD model by intraperitoneal injection of 30 mg/kg/day 1-Methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine hydrochloride (MPTP. HCL) for 5 consecutive days, and we created an in vitro PD model by injection of 100 μM 1-methyl-4-phenylpyridinium ion (MPP+) in primary microglia cells. Expression level of CD200/CD200R, inwardly rectifying potassium (Kir6.1/6.2), and sulfonylurea receptor (Sur1/2) were detected by Western blot (WB). Immunohistochemistry (IHC) was utilized to assess CD11b (microglia marker) and tyrosine hydroxylase (TH, a marker reveals dopamine level in neurons) expression levels. An in vitro PD model was applied to detect the influence of CD200 on ATP and inflammatory factors released from microglia. Interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-1β mRNA levels were explored by realtime quantitative polymerase chain reaction (RT-QPCR), and their protein levels were identified by enzyme-linked immunosorbent assay (ELISA).

Results

WB exhibited time-dependent down-regulation of CD200/CD200R in cerebra of PD mice compared to control mice, with Kir 6.1 and SUR 2 expressed mainly in microglia. IHC showed that CD11b reached a peak at the 1^st day after MPTP treatment, followed by time-dependent reduction, and TH decreased noticeably after MPTP induction. RT-QPCR demonstrated that compared with controls, IFN-γ, TNF-α, and IL-1β mRNA levels were significantly elevated at MPTP-1d, was reduced at MPTP-3d, and then returned to baseline at MPTP-7d. IHC showed that MPP+ significantly elevated microglia release of ATP. Similar to the effect of pinacidil (K+ channel opener), CD200 remarkably depressed MPP+-induced ATP release. ELISA showed that MPP+ significantly increased IFN-γ, TNF-α, and IL-1β release, and CD200 and pinacidil remarkably suppressed this elevation.

Conclusions

Our results show a novel role of CD200 in promoting opening of the KATP channel, inhibiting microglia activation and release of ATP, as well as inflammatory factors, thus protecting dopaminergic (DA) neurons against damage and alleviating PD.

Ethanol alters the expression of ion channel genes in Daphnia pulex

BACKGROUND

Heavy drinking can increase heart rate and blood glucose, induce hypoxic tolerance, impair brain cognitive functions, and alter gene expressions. These phenomena may occur even in response to small dose of ethanol exposure or during its withdrawal.

OBJECTIVES

To evaluate whether persistent low concentrations of ethanol exposure affect organism function and the gene expressions of ion channels.

METHODS

Daphnids were randomized to receive placebo 300 min, 2 mM ethanol 300 min, or 2 mM ethanol 240 min and then placebo 60 min. Heart rate, glucose levels, phototactic behavior, and hypoxic tolerance were recorded during experiment. At the end of the study, changes in the mRNA levels of ion channel genes were assessed in response to exposure to ethanol using quantitative polymerase chain reaction (PCR) techniques.

RESULTS

Heart rate was reversibly increased by ethanol withdrawal and returned to basal levels upon re-exposure to ethanol. Fifteen of 120 ion channel transcripts were affected by persistent ethanol exposure. Neither ethanol withdrawal nor persistent exposures showed an effect on blood glucose, phototactic behavior, or hypoxic tolerance.

CONCLUSIONS

Small doses of ethanol can increase heart rate and alter gene expression of multiple ion channels in Daphnia pulex. Affected ion channel genes may assist in understanding the mechanism of ethanol adaptation and tolerance.

Design, Synthesis, Acaricidal/Insecticidal Activity, and Structure-Activity Relationship Studies of Novel Oxazolines Containing Sulfone/Sulfoxide Groups Based on the Sulfonylurea Receptor Protein-Binding Site

Enormous compounds containing sulfone/sulfoxide groups have been used in a variety of fields, especially in drug and pesticide design. To search for novel environmentally benign and ecologically safe pesticides with unique modes of action, a series of 2,4-diphenyl-1,3-oxazolines containing sulfone/sulfoxide groups as chitin synthesis inhibitors (CSIs) were designed and synthesized on the basis of the sulfonylurea receptor protein-binding site for CSIs. Their structures were characterized by (1)H and (13)C nuclear magnetic resonance and high-resolution mass spectrometry. The acaricidal and insecticidal activities of the new compounds were evaluated. It was found that most of the target compounds displayed wonderful acaricidal activities against spider mite (Tetranychus cinnabarinus) larvae and eggs. Especially compounds I-4, II-3, and II-4 displayed higher activities than commercial etoxazole at a concentration of 2.5 mg L(-1). Some target compounds exhibited insecticidal activities against lepidopteran pests. The present work demonstrated that these compounds containing sulfone/sulfoxide groups could be considered as potential candidates for the development of novel acaricides in the future.

Regulation of myometrial contraction by ATP-sensitive potassium (KATP) channel via activation of SUR2B and Kir 6.2 in mouse

ATP-sensitive potassium (K_ATP) channels are well characterized in cardiac, pancreatic and many other muscle cells. In the present study, functional expression of the K_ATP channel was examined in non-pregnant murine longitudinal myometrium. Isometric contraction measurements and Western blot were used. K_ATP channel openers (KCOs), such as pinacidil, cromakalim, diazoxide and nicorandil, inhibited spontaneous myometrial contractions in a reversible and glibenclamide-sensitive manner. KCOs inhibited oxytocin (OXT)- and prostaglandin F_2α (PGF_2α)-induced phasic contractions in a glibenclamide-sensitive manner. SUR2B and Kir6.2 were detected by Western blot, whereas SUR1, SUR2A and Kir6.1 were not. These results show that pinacidl, cromakalim, diazoxide and nicorandil-sensitive K_ATP channels exist in murine myometrium, which are composed of SUR2B and Kir6.2. Based on the modulatory effects of the K_ATP channel on spontaneous contraction, OXT- and PGF_2α-induced contractions, K_ATP channels seem to play an essential role in murine myometrial motility via activation of SUR2B and Kir6.2.

Synthesis, characterization and biological evaluation of benzothiazoles and tetrahydrobenzothiazoles bearing urea or thiourea moieties as vasorelaxants and inhibitors of the insulin releasing process

A series of 1,3-benzothiazoles (series I) and 4,5,6,7-tetrahydro-1,3-benzothiazoles (series II) bearing an urea or a thiourea moiety at the 2-position were synthesized and tested as myorelaxants and inhibitors of insulin secretion. Several compounds (i.e. 13u and 13v) from series I showed a marked myorelaxant activity. Benzothiazoles bearing a strong electron withdrawing group (NO2, CN) at the 6-position and an alkyl group linked to the urea or the thiourea function at the 2-position were found to be the most potent compounds. The weak vasorelaxant activity of series II compounds evidenced the necessity of the presence of a complete aromatic heterocyclic system. The myorelaxant activity of some active compounds was reduced when measured on aorta rings precontracted by 80 mM KCl or by 30 mM KCl in the presence of 10 μM glibenclamide, suggesting the involvement of KATP channels in the vasorelaxant effect. Some compounds of series I tested on rat pancreatic islets provoked a marked inhibition of insulin secretion, among which 13a exhibited a clear tissue selectivity for pancreatic β-cells.

Isosteviol Sensitizes sarcKATP Channels towards Pinacidil and Potentiates Mitochondrial Uncoupling of Diazoxide in Guinea Pig Ventricular Myocytes

K_ATP channel is an important mediator or factor in physiological and pathological metabolic pathway. Activation of K_ATP channel has been identified to be a critical step in the cardioprotective mechanism against IR injury. On the other hand, desensitization of the channel to its opener or the metabolic ligand ATP in pathological conditions, like cardiac hypertrophy, would decrease the adaption of myocardium to metabolic stress and is a disadvantage for drug therapy. Isosteviol, obtained by acid hydrolysis of stevioside, has been demonstrated to play a cardioprotective role against diseases of cardiovascular system, like anti-IR injury, antihypertension, antihyperglycemia, and so forth. The present study investigated the effect of isosteviol (STV) on sarcK_ATP channel current induced by pinacidil and mitochondrial flavoprotein oxidation induced by diazoxide. Our results showed that preincubating cells with STV not only increased the current amplitude and activating rate of sarcK_ATP channels induced by pinacidil but also potentiated diazoxide-elicited oxidation of flavoprotein in mitochondria.

Ion channel macromolecular complexes in cardiomyocytes: roles in sudden cardiac death

The movement of ions across specific channels embedded on the membrane of individual cardiomyocytes is crucial for the generation and propagation of the cardiac electric impulse. Emerging evidence over the past 20 years strongly suggests that the normal electric function of the heart is the result of dynamic interactions of membrane ion channels working in an orchestrated fashion as part of complex molecular networks. Such networks work together with exquisite temporal precision to generate each action potential and contraction. Macromolecular complexes play crucial roles in transcription, translation, oligomerization, trafficking, membrane retention, glycosylation, post-translational modification, turnover, function, and degradation of all cardiac ion channels known to date. In addition, the accurate timing of each cardiac beat and contraction demands, a comparable precision on the assembly and organizations of sodium, calcium, and potassium channel complexes within specific subcellular microdomains, where physical proximity allows for prompt and efficient interaction. This review article, part of the Compendium on Sudden Cardiac Death, discusses the major issues related to the role of ion channel macromolecular assemblies in normal cardiac electric function and the mechanisms of arrhythmias leading to sudden cardiac death. It provides an idea of how these issues are being addressed in the laboratory and in the clinic, which important questions remain unanswered, and what future research will be needed to improve knowledge and advance therapy.

Ion Channels in the Heart

Optimal cardiac function depends on proper timing of excitation and contraction in various regions of the heart, as well as on appropriate heart rate. This is accomplished via specialized electrical properties of various components of the system, including the sinoatrial node, atria, atrioventricular node, His-Purkinje system, and ventricles. Here we review the major regionally determined electrical properties of these cardiac regions and present the available data regarding the molecular and ionic bases of regional cardiac function and dysfunction. Understanding these differences is of fundamental importance for the investigation of arrhythmia mechanisms and pharmacotherapy.

Antidiabetic agents and endothelial dysfunction - beyond glucose control

Diabetes is rapidly increasing worldwide, and the number of patients suffering from diabetes is projected to rise by 50% over the next 25 years, then affecting almost 600 million adults. Type 2 diabetes comprises 90-95% of all people with diabetes, and they constitute a patient group that carries a high burden of cardiovascular disease. The relationship between hyperglycaemia and macrovascular complications is still uncertain, at least in terms of the possibility of reducing cardiovascular events solely by improving glycaemic control. This MiniReview has thus focused on the effect of common antidiabetic agents, with emphasis on glucagon-like peptide-1, on the endothelial cells of the vasculature. Patients with type 2 diabetes suffer a two to four times higher risk of myocardial infarction and stroke than healthy persons. In addition to this, patients with diabetes have an increased atherosclerotic burden. Endothelial dysfunction is thought to be an early and important predictor of atherosclerosis and cardiovascular disease, and in people with type 2 diabetes, endothelial dysfunction is a common finding. It is therefore of importance to consider whether drugs used within the clinical management of Type 2 diabetes mellitus (T2DM) exert direct and positive effects on the vasculature independent of their glucose-lowering ability. This might serve to limit the adverse consequences of the macrovascular complications of T2DM, as dysfunction of endothelial cells is believed to contribute to a premature development of atherosclerosis.

Glibenclamide for the treatment of ischemic and hemorrhagic stroke

Ischemic and hemorrhagic strokes are associated with severe functional disability and high mortality. Except for recombinant tissue plasminogen activator, therapies targeting the underlying pathophysiology of central nervous system (CNS) ischemia and hemorrhage are strikingly lacking. Sur1-regulated channels play essential roles in necrotic cell death and cerebral edema following ischemic insults, and in neuroinflammation after hemorrhagic injuries. Inhibiting endothelial, neuronal, astrocytic and oligodendroglial sulfonylurea receptor 1-transient receptor potential melastatin 4 (Sur1-Trpm4) channels and, in some cases, microglial KATP (Sur1-Kir6.2) channels, with glibenclamide is protective in a variety of contexts. Robust preclinical studies have shown that glibenclamide and other sulfonylurea agents reduce infarct volumes, edema and hemorrhagic conversion, and improve outcomes in rodent models of ischemic stroke. Retrospective studies suggest that diabetic patients on sulfonylurea drugs at stroke presentation fare better if they continue on drug. Additional laboratory investigations have implicated Sur1 in the pathophysiology of hemorrhagic CNS insults. In clinically relevant models of subarachnoid hemorrhage, glibenclamide reduces adverse neuroinflammatory and behavioral outcomes. Here, we provide an overview of the preclinical studies of glibenclamide therapy for CNS ischemia and hemorrhage, discuss the available data from clinical investigations, and conclude with promising preclinical results that suggest glibenclamide may be an effective therapeutic option for ischemic and hemorrhagic stroke.