K(ATP) channel opener diazoxide prevents neurodegeneration: a new mechanism of action via antioxidative pathway activation

Timed sulfonylurea modulation improves locomotor and sensory dysfunction following spinal cord injury

Traumatic spinal cord injury (SCI) results in immediate tissue necrosis and delayed secondary expansion of neurological damage, often resulting in lifelong paralysis, neurosensory dysfunction, and chronic pain. Progressive hemorrhagic necrosis (PHN) and excessive excitation are the main sources of secondary neural injury. Recent approaches to attenuate PHN by glibenclamide can improve locomotor function after SCI. However, use of glibenclamide can exacerbate development of SCI-induced chronic pain by inhibiting KATP channels to increase neuronal excitation and glial activation. In this study, we explored a treatment strategy involving administration of glibenclamide, which suppresses PHN, and diazoxide, which protects against neuronal excitation and inflammation, at different time intervals following spinal cord contusion. Our goal was to determine whether this combined approach enhances both sensory and motor function. Contusive SCI was induced at spinal segment T10 in adult rats. We found that KATP channels opener, diazoxide, decreased the hyperexcitability of primary sensory neurons after SCI by electrophysiology. Timed application of glibenclamide and diazoxide following contusion significantly improved locomotor function and mitigated development of SCI-induced chronic pain, as shown by behavioral evidence. Finally, we found that timed application of glibenclamide and diazoxide attenuates the inflammatory activity in the spinal cord and increases the survival of spinal matters following SCI. These preclinical studies introduce a promising potential treatment strategy to address SCI-induced dysfunction.

Gliclazide Ameliorates Neuronal Injury by Attenuating Oxidative Stress in D-gal-Induced Senescent Cells and Aging Mice

Enhancement of oxidative stress and resultant neuronal injury play important roles in initiating cognitive impairment during the aging process. Thus, attenuating oxidative injury is regarded as a profitable therapeutic strategy for age-associated cognitive impairment. Previous studies showed that gliclazide (Gli) had a protective role in neuronal injury from cerebral ischemia/reperfusion (I/R) injury. However, whether Gli has a profitable effect on age-associated cognitive impairment remains largely unclear. The present study showed that Gli held the potential to attenuate neuronal apoptosis in D-gal-induced senescent cells and aging mice. Additionally, Gli could alleviate synaptic injury and cognitive function in D-gal-induced aging mice. Further study showed that Gli could attenuate oxidative stress in D-gal-induced senescent cells and aging mice. The p38 MAPK pathway was predicted as the downstream target of Gli retarding oxidative stress using in silico analysis. Further studies revealed that Gli attenuated D-gal-induced phosphorylation of p38 and facilitated Nrf2 nuclear expression, indicating that the anti-oxidative property of Gli may be associated with the p38 MAPK pathway. The study demonstrates that Gli has a beneficial effect on ameliorating D-gal-induced neuronal injury and cognitive impairment, making this compound a promising agent for the prevention and treatment of age-associated cognitive impairment.

Network medicine informed multi-omics integration identifies drug targets and repurposable medicines for Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a devastating, immensely complex neurodegenerative disease by lack of effective treatments. To date, the challenge to establishing effective treatment for ALS remains formidable, partly due to inadequate translation of existing human genetic findings into actionable ALS-specific pathobiology for subsequent therapeutic development. This study evaluates the feasibility of network medicine methodology via integrating human brain-specific multi-omics data to prioritize drug targets and repurposable treatments for ALS. Using human brain-specific genome-wide quantitative trait loci (x-QTLs) under a network-based deep learning framework, we identified 105 putative ALS-associated genes enriched in various known ALS pathobiological pathways, including regulation of T cell activation, monocyte differentiation, and lymphocyte proliferation. Specifically, we leveraged non-coding ALS loci effects from genome-wide associated studies (GWAS) on brain-specific expression quantitative trait loci (QTL) (eQTL), protein QTLs (pQTL), splicing QTL (sQTL), methylation QTL (meQTL), and histone acetylation QTL (haQTL). Applying network proximity analysis of predicted ALS-associated gene-coding targets and existing drug-target networks under the human protein-protein interactome (PPI) model, we identified a set of potential repurposable drugs (including Diazoxide, Gefitinib, Paliperidone, and Dimethyltryptamine) for ALS. Subsequent validation established preclinical and clinical evidence for top-prioritized repurposable drugs. In summary, we presented a network-based multi-omics framework to identify potential drug targets and repurposable treatments for ALS and other neurodegenerative disease if broadly applied.

Hyperinsulinism May Be Underreported in Hypoglycemic Patients with Phosphomannomutase 2 Deficiency

Objective

Phosphomannomutase 2 deficiency (PMM2-CDG) is a disorder of protein N-glycosylation with a wide clinical spectrum. Hypoglycemia is rarely reported in PMM2-CDG. In this study, we evaluated cause, treatment options and outcomes in cases with hypoglycemia in the course of PMM2-CDG.

Methods

Clinical records of patients followed with PMM2-CDG within the last two decades were reviewed. Medical data of patients with hypoglycemia were evaluated in more detail. Demographic and clinical findings, organ involvement and laboratory investigations at time of hypoglycemia were recorded. Time of first attack of hypoglycemia, cause, treatment modalities, duration of hypoglycemia (permanent/transient), and duration of treatment, as well as outcome were also recorded. Other published cases with PMM2-CDG and hypoglycemia are also reviewed in order to elucidate characteristics as well as pathophysiology of hypoglycemia.

Results

Nine patients with PMM2-CDG were reviewed, and hypoglycemia was present in three cases. All three had hyperinsulinism as the cause of hypoglycemia. In the first two cases reported here, serum insulin level concurrent with hypoglycemic episodes was elevated, and glucose response was exaggerated during glucagon test, favoring hyperinsulinism. However, in the third case, the serum insulin level at time of hypoglycemia was not so high but hypoglycemia responded well to diazoxide. Hyperinsulinism was permanent in two of these three cases. No genotype-phenotype correlation was observed with respect to hyperinsulinism.

Conclusion

The main cause of hypoglycemia in PMM2-CDG appears to be hyperinsulinism. Although insulin levels at the time of hypoglycemia may not be very high, hypoglycemia in patients with PMM2 responds well to diazoxide.

Somatostatin-evoked Aβ catabolism in the brain: Mechanistic involvement of α-endosulfine-KATP channel pathway

Alzheimer's disease (AD) is characterized by the deposition of amyloid β peptide (Aβ) in the brain. The neuropeptide somatostatin (SST) regulates Aβ catabolism by enhancing neprilysin (NEP)-catalyzed proteolytic degradation. However, the mechanism by which SST regulates NEP activity remains unclear. Here, we identified α-endosulfine (ENSA), an endogenous ligand of the ATP-sensitive potassium (KATP) channel, as a negative regulator of NEP downstream of SST signaling. The expression of ENSA is significantly increased in AD mouse models and in patients with AD. In addition, NEP directly contributes to the degradation of ENSA, suggesting a substrate-dependent feedback loop regulating NEP activity. We also discovered the specific KATP channel subtype that modulates NEP activity, resulting in the Aβ levels altered in the brain. Pharmacological intervention targeting the particular KATP channel attenuated Aβ deposition, with impaired memory function rescued via the NEP activation in our AD mouse model. Our findings provide a mechanism explaining the molecular link between KATP channel and NEP activation, and give new insights into alternative strategies to prevent AD.

The 40-Hz White Light-Emitting Diode (LED) Improves the Structure-Function of the Brain Mitochondrial KATP Channel and Respiratory Chain Activities in Amyloid Beta Toxicity

It has been described that using noninvasive exposure to 40-Hz white light LED reduces amyloid-beta, a peptide thought to initiate neurotoxic events in Alzheimer's disease (AD). However, the mechanisms remain to be identified. Since AD impairs mitochondrial potassium channels and respiratory chain activity, the objectives of the current study were to determine the effect of 40-Hz white light LED on structure-function of mitoK_ATP channel and brain mitochondrial respiratory chain activity, production of reactive oxygen species (ROS), and ΔΨ_m in AD. Single mitoK_ATP channel was considered using a channel incorporated into the bilayer lipid membrane and expression of mitoK_ATP-Kir6.1 subunit as a pore-forming subunit of the channel was determined using a western blot analysis in Aβ1-42 toxicity and light-treated rats. Our results indicated a severe decrease in mito-K_ATP channel permeation and Kir6.1 subunit expression coming from the Aβ1-42-induced neurotoxicity. Furthermore, we found that Aβ1-42-induced neurotoxicity decreased activities of complexes I and IV and increased ROS production and ΔΨ_m. Surprisingly, light therapy increased channel permeation and mitoK_ATP-Kir6.1 subunit expression. Noninvasive 40-Hz white light LED treatment also increased activities of complexes I and IV and decreased ROS production and ΔΨ_m up to ~ 70%. Here, we report that brain mito-K_ATP channel and respiratory chain are, at least in part, novel targets of 40-Hz white light LED therapy in AD.

Kir6.2-deficient mice develop somatosensory dysfunction and axonal loss in the peripheral nerves

Glucose-responsive ATP-sensitive potassium channels (K_ATP) are expressed in a variety of tissues including nervous systems. The depolarization of the membrane potential induced by glucose may lead to hyperexcitability of neurons and induce excitotoxicity. However, the roles of K_ATP in the peripheral nervous system (PNS) are poorly understood. Here, we determine the roles of K_ATP in the PNS using K_ATP-deficient (Kir6.2-deficient) mice. We demonstrate that neurite outgrowth of dorsal root ganglion (DRG) neurons was reduced by channel closers sulfonylureas. However, a channel opener diazoxide elongated the neurite. K_ATP subunits were expressed in mouse DRG, and expression of certain subunits including Kir6.2 was increased in diabetic mice. In Kir6.2-deficient mice, the current perception threshold, thermal perception threshold, and sensory nerve conduction velocity were impaired. Electron microscopy revealed a reduction of unmyelinated and small myelinated fibers in the sural nerves. In conclusion, K_ATP may contribute to the development of peripheral neuropathy.

Failed, Interrupted, or Inconclusive Trials on Neuroprotective and Neuroregenerative Treatment Strategies in Multiple Sclerosis: Update 2015-2020

In the recent past, a plethora of drugs have been approved for the treatment of multiple sclerosis (MS). These therapeutics are mainly confined to immunomodulatory or immunosuppressive strategies but do not sufficiently address remyelination and neuroprotection. However, several neuroregenerative agents have shown potential in pre-clinical research and entered Phase I to III clinical trials. Although none of these compounds have yet proceeded to approval, understanding the causes of failure can broaden our knowledge about neuroprotection and neuroregeneration in MS. Moreover, most of the investigated approaches are characterised by consistent mechanisms of action and proved convincing efficacy in animal studies. Therefore, learning from their failure will help us to enforce the translation of findings acquired in pre-clinical studies into clinical application. Here, we summarise trials on MS treatment published since 2015 that have either failed or were interrupted due to a lack of efficacy, adverse events, or for other reasons. We further outline the rationale underlying these drugs and analyse the background of failure to gather new insights into MS pathophysiology and optimise future study designs. For conciseness, this review focuses on agents promoting remyelination and medications with primarily neuroprotective properties or unconventional approaches. Failed clinical trials that pursue immunomodulation are presented in a separate article.

Ions, the Movement of Water and the Apoptotic Volume Decrease

The movement of water across the cell membrane is a natural biological process that occurs during growth, cell division, and cell death. Many cells are known to regulate changes in their cell volume through inherent compensatory regulatory mechanisms. Cells can sense an increase or decrease in their cell volume, and compensate through mechanisms known as a regulatory volume increase (RVI) or decrease (RVD) response, respectively. The transport of sodium, potassium along with other ions and osmolytes allows the movement of water in and out of the cell. These compensatory volume regulatory mechanisms maintain a cell at near constant volume. A hallmark of the physiological cell death process known as apoptosis is the loss of cell volume or cell shrinkage. This loss of cell volume is in stark contrast to what occurs during the accidental cell death process known as necrosis. During necrosis, cells swell or gain water, eventually resulting in cell lysis. Thus, whether a cell gains or loses water after injury is a defining feature of the specific mode of cell death. Cell shrinkage or the loss of cell volume during apoptosis has been termed apoptotic volume decrease or AVD. Over the years, this distinguishing feature of apoptosis has been largely ignored and thought to be a passive occurrence or simply a consequence of the cell death process. However, studies on AVD have defined an underlying movement of ions that result in not only the loss of cell volume, but also the activation and execution of the apoptotic process. This review explores the role ions play in controlling not only the movement of water, but the regulation of apoptosis. We will focus on what is known about specific ion channels and transporters identified to be involved in AVD, and how the movement of ions and water change the intracellular environment leading to stages of cell shrinkage and associated apoptotic characteristics. Finally, we will discuss these concepts as they apply to different cell types such as neurons, cardiomyocytes, and corneal epithelial cells.

Mitochondrial KATP channels contribute to the protective effects of hydrogen sulfide against impairment of central chemoreception of rat offspring exposed to maternal cigarette smoke

We previously reported that maternal cigarette smoke (CS) exposure resulted in impairment of central chemoreception and induced mitochondrial dysfunction in offspring parafacial respiratory group (pFRG), the kernel for mammalian central chemoreception. We also found that hydrogen sulfide (H₂S) could attenuate maternal CS exposure-induced impairment of central chemoreception in the rat offspring in vivo. Mitochondrial ATP sensitive potassium (mitoK_ATP) channel has been reported to play a significant role in mitochondrial functions and protect against apoptosis in neurons. Thus, we hypothesize here that mitoK_ATP channel plays a role in the protective effects of H₂S on neonatal central chemoreception in maternal CS-exposed rats. Our findings revealed that pretreatment with NaHS (donor of H₂S, 22.4mM) reversed the central chemosensitivity decreased by maternal CS exposure, and also inhibited cell apoptosis in offspring pFRG, however, 5-HD (blocker of mitoK_ATP channels, 19mM) attenuated the protective effects of NaHS. In addition, NaHS declined pro-apoptotic proteins related to mitochondrial pathway apoptosis in CS rat offspring pFRG, such as Bax, Cytochrome C, caspase9 and caspase3. NaHS or 5-HD alone had no significant effect on above indexes. These results suggest that mitoK_ATP channels play an important role in the protective effect of H₂S against impairment of central chemoreception via anti-apoptosis in pFRG of rat offspring exposed to maternal CS.

Hypoglycemia in CDG patients due to PMM2 mutations: Follow up on hyperinsulinemic patients

BACKGROUND

Phosphomannomutase 2 deficiency (PMM2-CDG) is the most common congenital disorder of glycosylation (CDG). Hypoglycemia has been reported in various CDG including PMM2-CDG. The frequency and etiology of hypoglycemia in PMM2-CDG are not well studied.

METHODS

We conducted a systematic review of the literature on genetically and/or biochemically confirmed PMM2-CDG patients who developed hypoglycemia. Prospective follow-up information on the patients who received diazoxide therapy was collected and evaluated.

RESULTS

A total of 165 peer-reviewed articles reporting on 933 PMM2-CDG patients were assessed. Hypoglycemia was specifically mentioned only in 23 of these patients (2.5%). Hyperinsulinism was identified in 10 patients (43% of all hypoglycemic patients). Among these 10 patients, seven were successfully treated with diazoxide. However, most patients remained on therapy longer than a year to stay free of hypoglycemia.

CONCLUSION

Hypoglycemia is a rarely reported finding in patients with PMM2-CDG. Diazoxide-responsive hyperinsulinism was found to have a good prognosis on medication in our PMM2-CDG patients with hypoglycemia. No genotype-phenotype correlation was observed with respect to hyperinsulinism. A prospective study should be undertaken to explore the hypothesis that hypoglycemia is underdiagnosed in PMM2-CDG and to evaluate whether hyperinsulinism is always associated with hypoglycemia.

Health Risks of Hypovitaminosis D: A Review of New Molecular Insights

Hypovitaminosis D has become a pandemic, being observed in all ethnicities and age groups worldwide. Environmental factors, such as increased air pollution and reduced ultraviolet B (UVB) irradiation, as well as lifestyle factors, i.e., decreased outdoor activities and/or poor intake of vitamin D-rich food, are likely involved in the etiology of a dramatic reduction of vitamin D circulating levels. The insufficiency/deficiency of vitamin D has long been known for its association with osteoporosis and rickets. However, in the last few decades it has become a serious public health concern since it has been shown to be independently associated with various chronic pathological conditions such as cancer, coronary heart disease, neurological diseases, type II diabetes, autoimmune diseases, depression, with various inflammatory disorders, and with increased risk for all-cause mortality in the general population. Prevention strategies for these disorders have recently involved supplementation with either vitamin D2 or vitamin D3 or their analogs at required daily doses and tolerable upper-limit levels. This review will focus on the emerging evidence about non-classical biological functions of vitamin D in various disorders.

KATP Channel Expression and Genetic Polymorphisms Associated with Progression and Survival in Amyotrophic Lateral Sclerosis

The ATP-sensitive potassium (K_ATP) channel directly regulates the microglia-mediated inflammatory response following CNS injury. To determine the putative role of the K_ATP channel in amyotrophic lateral sclerosis (ALS) pathology, we investigated whether ALS induces changes in K_ATP channel expression in the spinal cord and motor cortex. We also characterized new functional variants of human ABCC8, ABCC9, KCNJ8, and KCNJ11 genes encoding for the K_ATP channel and analyzed their association with ALS risk, rate of progression, and survival in a Spanish ALS cohort. The expression of ABCC8 and KCNJ8 genes was enhanced in the spinal cord of ALS samples, and KCNJ11 increased in motor cortex of ALS samples, as determined by real-time polymerase chain reaction. We then sequenced the exons and regulatory regions of K_ATP channel genes from a subset of 28 ALS patients and identified 50 new genetic variants. For the case-control association analysis, we genotyped five selected polymorphisms with predicted functional relevance in 185 Spanish ALS (134 spinal ALS and 51 bulbar ALS) patients and 493 controls. We found that bulbar ALS patients presenting the G/G genotype of the rs4148646 variant of ABCC8 and the T/T genotype of the rs5219 variant of KCNJ11 survived longer than other ALS patients presenting other genotypes. Also, the C/C genotype of the rs4148642 variant of ABCC8 and the T/C genotype of the rs148416760 variant of ABCC9 modified the progression rate in spinal ALS patients. Our results suggest that the K_ATP channel plays a role in the pathophysiological mechanisms of ALS.

Hypoglycemia in the preterm neonate: etiopathogenesis, diagnosis, management and long-term outcomes

Glucose, like oxygen, is of fundamental importance for any living being and it is the major energy source for the fetus and the neonate during gestation. The placenta ensures a steady supply of glucose to the fetus, while birth marks a sudden change in substrate delivery and a major change in metabolism. Hypoglycemia is one of the most common pathologies encountered in the neonatal intensive care unit and affects a wide range of neonates. Preterm, small for gestational age (GA) and intra-uterine growth restricted neonates are especially vulnerable due to their lack of metabolic reserves and associated co-morbidities. Nearly 30-60% of these high-risk infants are hypoglycemic and require immediate intervention. Preterm neonates are uniquely predisposed to developing hypoglycemia and its associated complications due to their limited glycogen and fat stores, inability to generate new glucose using gluconeogenesis pathways, have higher metabolic demands due to a relatively larger brain size, and are unable to mount a counter-regulatory response to hypoglycemia. In this review we will discuss the epidemiology; pathophysiology; clinical presentation; management and neurodevelopmental outcomes in affected infants and summarize evidence to develop a rational and scientific approach to this common problem.

Molecular Bases of Brain Preconditioning

Preconditioning of the brain induces tolerance to the damaging effects of ischemia and prevents cell death in ischemic penumbra. The development of this phenomenon is mediated by mitochondrial adenosine triphosphate-sensitive potassium (KATP+) channels and nitric oxide signaling (NO). The aim of this study was to investigate the dynamics of molecular changes in mitochondria after ischemic preconditioning (IP) and the effect of pharmacological preconditioning (PhP) with the KATP+-channels opener diazoxide on NO levels after ischemic stroke in rats. Immunofluorescence-histochemistry and laser-confocal microscopy were applied to evaluate the cortical expression of electron transport chain enzymes, mitochondrial KATP+-channels, neuronal and inducible NO-synthases, as well as the dynamics of nitrosylation and nitration of proteins in rats during the early and delayed phases of IP. NO cerebral content was studied with electron paramagnetic resonance (EPR) spectroscopy using spin trapping. We found that 24 h after IP in rats, there is a two-fold decrease in expression of mitochondrial KATP+-channels (p = 0.012) in nervous tissue, a comparable increase in expression of cytochrome c oxidase (p = 0.008), and a decrease in intensity of protein S-nitrosylation and nitration (p = 0.0004 and p = 0.001, respectively). PhP led to a 56% reduction of free NO concentration 72 h after ischemic stroke simulation (p = 0.002). We attribute this result to the restructuring of tissue energy metabolism, namely the provision of increased catalytic sites to mitochondria and the increased elimination of NO, which prevents a decrease in cell sensitivity to oxygen during subsequent periods of severe ischemia.

Effects of diazoxide in experimental acute necrotizing pancreatitis

OBJECTIVE:

We aimed to assess the effects of diazoxide on the mortality, pancreatic injury, and inflammatory response in an experimental model of acute pancreatitis.

METHODS:

Male Wistar rats (200-400 g) were divided randomly into two groups. Fifteen minutes before surgery, animals received physiological (0.9%) saline (3 mL/kg) (control group) or 45 mg/kg diazoxide (treatment group) via the intravenous route. Acute pancreatitis was induced by injection of 2.5% sodium taurocholate via the biliopancreatic duct. Mortality (n=38) was observed for 72 h and analyzed by the Mantel-Cox Log-rank test. To study pancreatic lesions and systemic inflammation, rats (10 from each group) were killed 3 h after acute pancreatitis induction; ascites volume was measured and blood as well as pancreases were collected. Pancreatic injury was assessed according to Schmidt's scale. Cytokine expression in plasma was evaluated by the multiplex method.

RESULTS:

Mortality at 72 h was 33% in the control group and 60% in the treatment group (p=0.07). Ascites volumes and plasma levels of cytokines between groups were similar. No difference was observed in edema or infiltration of inflammatory cells in pancreatic tissues from either group. However, necrosis of acinar cells was lower in the treatment group compared to the control group (3.5 vs. 3.75, p=0.015).

CONCLUSIONS:

Treatment with diazoxide can reduce necrosis of acinar cells in an experimental model of acute pancreatitis, but does not affect the inflammatory response or mortality after 72 h.

Converging roles of ion channels, calcium, metabolic stress, and activity pattern of Substantia nigra dopaminergic neurons in health and Parkinson's disease

Dopamine‐releasing neurons within the Substantia nigra (SN DA) are particularly vulnerable to degeneration compared to other dopaminergic neurons. The age‐dependent, progressive loss of these neurons is a pathological hallmark of Parkinson's disease (PD), as the resulting loss of striatal dopamine causes its major movement‐related symptoms. SN DA neurons release dopamine from their axonal terminals within the dorsal striatum, and also from their cell bodies and dendrites within the midbrain in a calcium‐ and activity‐dependent manner. Their intrinsically generated and metabolically challenging activity is created and modulated by the orchestrated function of different ion channels and dopamine D2‐autoreceptors. Here, we review increasing evidence that the mechanisms that control activity patterns and calcium homeostasis of SN DA neurons are not only crucial for their dopamine release within a physiological range but also modulate their mitochondrial and lysosomal activity, their metabolic stress levels, and their vulnerability to degeneration in PD. Indeed, impaired calcium homeostasis, lysosomal and mitochondrial dysfunction, and metabolic stress in SN DA neurons represent central converging trigger factors for idiopathic and familial PD. We summarize double‐edged roles of ion channels, activity patterns, calcium homeostasis, and related feedback/feed‐forward signaling mechanisms in SN DA neurons for maintaining and modulating their physiological function, but also for contributing to their vulnerability in PD‐paradigms. We focus on the emerging roles of maintained neuronal activity and calcium homeostasis within a physiological bandwidth, and its modulation by PD‐triggers, as well as on bidirectional functions of voltage‐gated L‐type calcium channels and metabolically gated ATP‐sensitive potassium (K‐ATP) channels, and their probable interplay in health and PD.

We propose that SN DA neurons possess several feedback and feed‐forward mechanisms to protect and adapt their activity‐pattern and calcium‐homeostasis within a physiological bandwidth, and that PD‐trigger factors can narrow this bandwidth. We summarize roles of ion channels in this view, and findings documenting that both, reduced as well as elevated activity and associated calcium‐levels can trigger SN DA degeneration.

This article is part of a special issue on Parkinson disease.

Oxidation of ion channels in the aging nervous system

Ion channels are integral membrane proteins that allow passive diffusion of ions across membranes. In neurons and in other excitable cells, the harmonious coordination between the numerous types of ion channels shape and propagate electrical signals. Increased accumulation of reactive oxidative species (ROS), and subsequent oxidation of proteins, including ion channels, is a hallmark feature of aging and may contribute to cell failure as a result. In this review we discuss the effects of ROS on three major types of ion channels of the central nervous system, namely the potassium (K(+)), calcium (Ca(2+)) and sodium (Na(+)) channels. We examine two general mechanisms through which ROS affect ion channels: via direct oxidation of specific residues and via indirect interference of pathways that regulate the channels. The overall status of the present studies indicates that the interaction of ion channels with ROS is multimodal and pervasive in the central nervous system and likely constitutes a general mechanism of aging susceptibility.

Effects of diazoxide on Aβ1-42-induced expression of the NR2B subunit in cultured cholinergic neurons

The accumulation of amyloid-β protein (Aβ) is significant in the pathogenesis of Alzheimer's disease. Several previous studies indicate that the NR2B‑containing N‑methyl‑D‑aspartate receptors are critically involved in the Aβ mediated disruption of neuronal function. Diazoxide (DZ), a highly selective drug capable of opening mitochondrial ATP‑sensitive potassium channels, has neuroprotective effects against neuronal cell death. However, the mechanism by which DZ protects cholinergic neurons against Aβ‑induced cytotoxicity remains to be elucidated. The present study was designed to investigate the effects of DZ pretreatment against Aβ1‑42‑induced expression of NR2B in order to gain novel insights into the neuroprotective mechanisms. Following exposure to Aβ1‑42 for 24 h, the expression of the NR2B subunit remained unchanged compared with the control group. However, a significant increase in the expression of the NR2B subunit was observed following treatment with Aβ1‑42 for 72 h (P<0.05); and the upregulation of the expression of the NR2B subunit was reversed by pretreatment with DZ (P<0.05). These results suggested that DZ may counteract Aβ1‑42‑mediated cytotoxicity by alleviating the expression of NR2B.

Diazoxide preconditioning of endothelial progenitor cells from streptozotocin-induced type 1 diabetic rats improves their ability to repair diabetic cardiomyopathy

Type 1 diabetes mellitus (DM) is a strong risk factor for the development of diabetic cardiomyopathy (DCM) which is the leading cause of morbidity and mortality in the type 1 diabetic patients. Stem cells may act as a therapeutic agent for the repair of DCM. However, deteriorated functional abilities and survival of stem cells derived from type 1 diabetic subjects need to be overcome for obtaining potential outcome of the stem cell therapy. Diazoxide (DZ) a highly selective mitochondrial ATP-sensitive K(+) channel opener has been previously shown to improve the ability of mesenchymal stem cells for the repair of heart failure. In the present study, we evaluated the effects of DZ preconditioning in improving the ability of streptozotocin-induced type 1 diabetes affected bone marrow-derived endothelial progenitor cells (DM-EPCs) for the repair of DCM in the type 1 diabetic rats. DM-EPCs were characterized by immunocytochemistry, flow cytometry, and reverse transcriptase PCR for endothelial cell-specific markers like vWF, VE cadherin, VEGFR2, PECAM, CD34, and eNOS. In vitro studies included preconditioning of DM-EPCs with 200 μM DZ for 30 min followed by exposure to either 200 μM H2O2 for 2 h (for oxidative stress induction) or 30 mM glucose media (for induction of hyperglycemic stress) for 48 h. Non-preconditioned EPCs with and without exposure to H2O2 and 30 mM high glucose served as controls. These cells were then evaluated for survival (by MTT and XTT cell viability assays), senescence, paracrine potential (by ELISA for VEGF), and alteration in gene expression [VEGF, stromal derived factor-1α (SDF-1α), HGF, bFGF, Bcl2, and Caspase-3]. DZ preconditioned DM-EPCs demonstrated significantly increased survival and VEGF release while reduced cell injury and senescence. Furthermore, DZ preconditioned DM-EPCs exhibited up-regulated expression of prosurvival genes (VEGF, SDF-1α, HGF, bFGF, and Bcl2) on exposure to H2O2, and VEGF and Bcl2 on exposure to hyperglycemia while down regulation of Caspase-3 gene. Eight weeks after type 1 diabetes induction, DZ preconditioned, and non-preconditioned DM-EPCs were transplanted into left ventricle of diabetic rats (at a dose of 2 × 10(6) DM-EPCs/70 μl serum free medium). After 4 weeks, DZ preconditioned DM-EPCs transplantation improved cardiac function as assessed by Millar's apparatus. There was decrease in collagen content estimated by Masson's trichrome and sirius red staining. Furthermore, reduced cell injury was observed as evidenced by decreased expression of Caspase-3 and increased expression of prosurvival genes Bcl2, VEGF, and bFGF by semi-quantitative real-time PCR. In conclusion, the present study demonstrated that DZ preconditioning enhanced EPCs survival under oxidative and hyperglycemic stress and their ability to treat DCM.

Effects of diazoxide in multiple sclerosis: A randomized, double-blind phase 2 clinical trial

Objective:

The aim of this study was to test the safety of diazoxide and to search for signs of efficacy in patients with relapsing-remitting multiple sclerosis (RRMS).

Methods:

In this multicenter, randomized, placebo-controlled, double-blind trial (treatment allocation was concealed), 102 patients with RRMS were randomized to receive a daily oral dose of diazoxide (0.3 and 4 mg/d) or placebo for 24 weeks (NCT01428726). The primary endpoint was the cumulative number of new T1 gadolinium-enhancing lesions per patient, recorded every 4 weeks from week 4 to week 24. Secondary endpoints included brain MRI variables such as the number of new/enlarging T2 lesions and the percentage brain volume change (PBVC); clinical variables such as the percentage of relapse-free patients, relapse rate, and change in the Expanded Disability Status Scale score; and safety and tolerability.

Results:

Diazoxide was well-tolerated and it produced no serious adverse events other than 1 case of Hashimoto disease. At the 2 doses tested, diazoxide did not improve the primary endpoint or the MRI and clinical variables related to the presence of new lesions or relapses. Patients treated with diazoxide showed reduced PBVC compared with the placebo group, although such changes could be confounded by the higher disease activity of the treated group and the vascular effects of diazoxide.

Conclusion:

At the doses tested, oral diazoxide did not decrease the appearance of new lesions evident by MRI. The effects in slowing the progression of brain atrophy require further validation.

Classification of evidence:

This study provides Class I evidence that for patients with RRMS, diazoxide (0.3 and 4 mg/d) does not significantly change the number of new MRI T1 gadolinium-enhancing lesions.

The interplay between metabolic homeostasis and neurodegeneration: insights into the neurometabolic nature of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal, neurodegenerative disease that is characterized by the selective degeneration of upper motor neurons and lower spinal motor neurons, resulting in the progressive paralysis of all voluntary muscles. Approximately 10 % of ALS cases are linked to known genetic mutations, with the remaining 90 % of cases being sporadic. While the primary pathology in ALS is the selective death of upper and lower motor neurons, numerous studies indicate that an imbalance in whole body and/or cellular metabolism influences the rate of progression of disease. This review summarizes current research surrounding the impact of impaired metabolic physiology in ALS. We extend ideas to consider prospects that lie ahead in terms of how metabolic alterations may impact the selective degeneration of neurons in ALS and how targeting of adenosine triphosphate-sensitive potassium (K_ATP) channels may represent a promising approach for obtaining neuroprotection in ALS.

Vitamin D cell signalling in health and disease

Vitamin D deficiency has been linked to many human diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), hypertension and cardiovascular disease. A Vitamin D phenotypic stability hypothesis, which is developed in this review, attempts to describe how this vital hormone acts to maintain healthy cellular functions. This role of Vitamin D as a guardian of phenotypic stability seems to depend on its ability to maintain the redox and Ca(2+) signalling systems. It is argued that its primary action is to maintain the expression of those signalling components responsible for stabilizing the low resting state of these two signalling pathways. This phenotypic stability role is facilitated through the ability of vitamin D to increase the expression of both Nrf2 and the anti-ageing protein Klotho, which are also major regulators of Ca(2+) and redox signalling. A decline in Vitamin D levels will lead to a decline in the stability of this regulatory signalling network and may account for why so many of the major diseases in man, which have been linked to vitamin D deficiency, are associated with a dysregulation in both ROS and Ca(2+) signalling.

Oxidative modulation of K+ channels in the central nervous system in neurodegenerative diseases and aging

SIGNIFICANCE

Oxidative stress and damage are well-established components of neurodegenerative diseases, contributing to neuronal death during disease progression. Here, we consider key K(+) channels as target proteins that can undergo oxidative modulation, describe what is understood about how this influences disease progression, and consider regulation of these channels by gasotransmitters as a means of cellular protection.

RECENT ADVANCES

Oxidative regulation of the delayed rectifier Kv2.1 and the Ca(2+)- and voltage-sensitive BK channel are established, but recent studies contest how their redox sensitivity contributes to altered excitability, progression of neurodegenerative diseases, and healthy aging.

CRITICAL ISSUES

Both Kv2.1 and BK channels have recently been established as target proteins for regulation by the gasotransmitters carbon monoxide and hydrogen sulfide. Establishing the molecular basis of such regulation, and exactly how this influences excitability and vulnerability to apoptotic cell death will determine whether such regulation can be exploited for therapeutic benefit.

FUTURE DIRECTIONS

Developing a more comprehensive picture of the oxidative modulation of K(+) channels (and, indeed, other ion channels) within the central nervous system in health and disease will enable us to better understand processes associated with healthy aging as well as distinct processes underlying progression of neurodegenerative diseases. Advances in the growing understanding of how gasotransmitters can regulate ion channels, including redox-sensitive K(+) channels, are a research priority for this field, and will establish their usefulness in design of future approaches for the treatment of such diseases.

KATP-channels play a minor role in the protective hypoxic shut-down of cerebellar activity in eider ducks (Somateria mollissima)

Eider duck (Somateria mollissima) cerebellar neurons are highly tolerant toward hypoxia in vitro, which in part is due to a hypoxia-induced depression of their spontaneous activity. We have studied whether this response involves ATP-sensitive potassium (KATP) channels, which are known to be involved in the hypoxic/ischemic defense of mammalian neural and muscular tissues, by causing hyperpolarization and reduced ATP demand. Extracellular recordings in the Purkinje layer of isolated normoxic eider duck cerebellar slices showed that their spontaneous neuronal activity decreased significantly compared to in control slices when the KATP channel opener diazoxide (600 μM) was added (F1,70=92.781, p<0.001). Adding the KATP channel blocker tolbutamide (400 μM) 5 min prior to diazoxide completely abolished its effect (F1,55=39.639, p<0.001), strongly suggesting that these drugs have a similar mode of action in this avian species as in mammals. The spontaneous activity of slices treated with tolbutamide in combined hypoxia/chemical anoxia (95% N2-5% CO2 and 2 mM NaCN) was not significantly different from that of control slices (F1,203=0.071, p=0.791). Recovery from hypoxia/anoxia was, however, slightly but significantly weaker in tolbutamide-treated slices than in control slices (F1,137=15.539, p<0.001). We conclude that KATP channels are present in eider duck cerebellar neurons and are activated in hypoxia/anoxia, but that they do not play a key role in the protective shut-down response to hypoxia/anoxia.

Diazoxide attenuates autoimmune encephalomyelitis and modulates lymphocyte proliferation and dendritic cell functionality

Activation of mitochondrial ATP-sensitive potassium (KATP) channels is postulated as an effective mechanism to confer cardio and neuroprotection, especially in situations associated to oxidative stress. Pharmacological activation of these channels inhibits glia-mediated neuroinflammation. In this way, diazoxide, an old-known mitochondrial KATP channel opener, has been proposed as an effective and safe treatment for different neurodegenerative diseases, demonstrating efficacy in different animal models, including the experimental autoimmune encephalomyelitis (EAE), an animal model for Multiple Sclerosis. Although neuroprotection and modulation of glial reactivity could alone explain the positive effects of diazoxide administration in EAE mice, little is known of its effects on the immune system and the autoimmune reaction that triggers the EAE pathology. The aim of the present work was to study the effects of diazoxide in autoimmune key processes related with EAE, such as antigen presentation and lymphocyte activation and proliferation. Results show that, although diazoxide treatment inhibited in vitro and ex-vivo lymphocyte proliferation from whole splenocytes it had no effect in isolated CD4(+) T cells. In any case, treatment had no impact in lymphocyte activation. Diazoxide can also slightly decrease CD83, CD80, CD86 and major histocompatibility complex class II expression in cultured dendritic cells, demonstrating a possible role in modulating antigen presentation. Taken together, our results indicate that diazoxide treatment attenuates autoimmune encephalomyelitis pathology without immunosuppressive effect.

Diazoxide pretreatment prevents Aβ1-42 induced oxidative stress in cholinergic neurons via alleviating NOX2 expression

The aggregation and accumulation of amyloid-β (Aβ) plays a significant role in the pathogenesis of Alzheimer's disease. Aβ is known to increase free radical production in neuronal cells, leading to oxidative stress and cell death. Diazoxide (DZ), a highly selective drug capable of opening mitochondrial ATP-sensitive potassium channels, has neuroprotective effects against neuronal cell death. However, the mechanism through which DZ protects cholinergic neurons against Aβ-induced oxidative injury is still unclear. The present study was designed to investigate the effects of DZ pretreatment against Aβ1-42 induced oxidative damage and cytotoxicity. Through measures of DZ effects on Aβ1-42 induced cellular damage, reactive oxygen species (ROS) and MDA generation and expressions of gp91phox and p47phox in cholinergic neurons, new insights into the neuroprotective mechanisms can be derived. Aβ1-42 significantly decreased 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide levels and increased ROS and MDA production; all effects were attenuated by pretreatment with DZ or diphenyleneiodonium chloride (a NOX2 inhibitor). Pretreatment with DZ also attenuated the upregulation of NOX2 subunits (gp91phox and p47phox) induced by Aβ1-42. Since NOX2 is one of the main sources of free radicals, these results suggest that DZ can counteract Aβ1-42 induced oxidative stress and associated cell death by reducing the level of ROS and MDA, in part, by alleviating NOX2 expression.

The role of glutamate and its receptors in multiple sclerosis

Glutamate is an excitatory neurotransmitter of the central nervous system, which has a central role in a complex communication network established between neurons, astrocytes, oligodendrocytes, and microglia. Multiple abnormal triggers such as energy deficiency, oxidative stress, mitochondrial dysfunction, and calcium overload can lead to abnormalities in glutamate signaling. Thus, the disturbance of glutamate homeostasis could affect practically all physiological functions and interactions of brain cells, leading to excitotoxicity. Excitotoxicity is the pathological process by which nerve cells are damaged or killed by excessive stimulation by glutamate. Although neuron degeneration and death are the ultimate consequences of multiple sclerosis (MS), it is now widely accepted that alterations in the function of surrounding glial cells are key features in the progression of the disease. The present knowledge raise the possibility that the modulation of glutamate release and transport, as well as receptors blockade or glutamate metabolism modulation, might be relevant targets for the development of future therapeutic interventions in MS.